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.

Extensions: add optional arguments to ThirdPartyPath

ThirdPartyPath("name", "path1", "path2") will resolve by default into "../name/path1/path2"

GCC BUILD: Prevent Memory Error when compiling huge projects.

Also deleted dead code.

MQTT WIP: intermediate state, added perfect hash to map topic to variables

MQTT WIP: intermediate state, implementing MQTT client C code generator.

WIP: Add skeleton for MQTT extension based on part of OPC-UA extension.

For now generated code makes no sense but persistently-configurable-C-generating-extension infrastructure is there.

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

C runtime: Fix PLCObject.hpp preventing build.

IDE: generalize EVT_GRID_CELL_CHANG{ING->ED} (WxPy4)

IDE: hopefully last fix about float type being passed to WxPy4.

IDE: enhance variable forcing contextual menu

IDE: fix completion

uses ctrl key on Mac
update internal variable list before listing them
avoid exception if empty list
apply selection when pressing return or enter

IDE: Workaround some reported WxPython/MacOS problems.

SetSelection should be used instead of SetStringSelection , and FindString must use case_sensitive=True

IDE: Fix search result not showing single occurrences

IDE: remove warning if editing location leads to no change

IDE: Use 8x8 grid by default