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

IDE: Fix exception when connecting complex types