Merge remote-tracking branch 'hggit/python3' into python3

IDE: Allow environment variable override in ThirdPartyPath, and use it also for matiec.

IDE: re-use eRPC URI definitions in connector factory.

Preparing for serial and US eRPC connection.

Cosmetic changes

IDE: refactor discovery panel / zeroconf

Bundle ZeroConf listener and interfaces changes monitor into separate module.
Prepare to extend with USB device browsing.

IDE: refactor ERPC URI editor, add serial and USB URI types

python runtime: update ServicePublisher to current Zeroconf API

eRPC: Backward compatibility with runtime versions missing GetVersions extended call.

eRPC: Version bump

python_runtime: fix ExtendedCall register/unregistering.

eRPC: Server closes connection on exception to prevent client to block until timeout when it happens.

Add ExtendedCall to PLCObject as a replacement of RemoteExec and reflect it in eRPC interface.

ExtendedCall is a generic remote procedure call that runtime code can register to and that IDE extensions can call.
For example a fieldbus extension can use ExtendedCall to browse the fieldbus devices connected to the runtime.

Removed dependency in requirements.txt.

TESTS: Update Matiec revision in GH workflow

MQTT: update test project to reflect latest changes

SVGHMI update generated XSLT

SVGHMI: remove widgets deprecated since long

SVGHMI: add ForEach widget example

SVGHMI: Extend ForEach widget to expose range, position and size in a way comparable with ScrollBar widget.

SVGHMI: code cleanup

MQTT: Add status global variable MQTT_STATUS_n, one per MQTT client

MQTT: strip unsupported types from type choice dropdown, better wrong type detection in build.

MQTT: remove debug prints

MQTT: add JSON fixed size 1D array support. WIP. Parsing array still broken.

MQTT: do not convert to UPPERCASE json keys.

MQTT: added support for strings in JSON payload only.

MQTT: remove accidentally committed debug printfs + cosmetic

MQTT: fix invocation of json_scanf (use pointers, not values...)

MQTT: fix bisection failing when topics start with same substring.

MQTT: Update available type choices when data types are changed in the IDE

MQTT: remove standalone MQTT clien generator code.

Code was inherited from OPC-UA extension, but not properly maintained.

MQTT: add JSON payload corresponding to IEC Structured types

- uses https://github.com/cesanta/frozen
- frozen.c is added as a resulting c file in generat_C (fix toolchain_gcc.py as it was breaking dependency checking)
- structured types are converted to C #define, in turn generating json_scanf and json_printf statements

MQTT: WIP supporting structured types : do not crash when generating C code if using location with no size

MQTT: add dropdown to select type assigned to a topic

MQTT+IDE: Allow user to associate IEC structure datatype to a topic.

IDE: allow structures to be located.

merge MQTT grafted from python2 branch - untested

MQTT: add test projects, to be later included in automated testing.

MQTT: add SSL support

SVGHMI: cosmetic

SVGHMI: Fix watchdog not cleanly restarting browser because not waiting for stop operation to finish before restarting.

MQTT: WIP, re-organized disconnection handling, now keep track of connection status and reconnect accordingly.

This fixes bug with non-reconnecting to broker when having no published variables.

MQTT: link to SSL only when needed.

IDE: Fix "Save" toolbar button and file menu entry not appearing when extension makes changes

MQTT: WIP fix modified status not being set when adding and modifying topics or attributes.

Fix loading of CSV that was not applying model types, and that not checking conformance either.

MQTT: WIP, PLC starts even if MQTT client can't connect broker, and publish+subscribe again when reconnecting.

MQTT: WIP, destroys paho client during failure handling at init and at cleanup. Use mutex to protect retrieve.

MQTT: Implements reconnecting in publish thread in case thread is waken-up but client is disconnected.

Note: paho's lostConnection callback got already disabled in previous commit.

MQTT: take C part away from python code for readability.

C lines change a bit because of unnecessary escaping for '\'.

MQTT: WIP, prevent crash after disconnect. Disable auto-reconnect on connection lost callback.

MQTT: Stop publish thread properly on PLC stop

MQTT: Fix overkill use of wx sizer

MQTT: Fix crash when browsing locations

MQTT: WIP. Added handling of received messages (subscriptions)

Dropped perfect hash in favor of bisection
Also fixed indentation (tabs)

MQTT: WIP, added publish thread waking-up when published variables change.

MQTT: WIP, subscibed topics have no "Retained" attribute.

Allow subscribed and published data models to be different, by removing "Retained" column.

MQTT: WIP, now publishes initial values at init.

MQTT: WIP, now connects to broker. Added MQTT 3 support and protocol version selection in IDE.

MQTT: (WIP) Fix OpenSSL linking.

MQTT: still WIP, generated C code builds and link.