Moved XSLT model query python code so that XSLT part can be reused for other transformations

Fixed unitialized parameter in instances_path stylesheet, leading to
calls to add_instance with no data when passing datatypes insteatd of project
root. That bug was making exceptions (for exemple when editing type) when
having arrays of derivated types in project.

Fixed code quality according to pep8 and pylint.

Fix exception on exit in some case, sequel of an earlier cleanup commit I couldn't find back. Disconnecting the event is apparently the way to go. https://wiki.wxpython.org/Surviving%20with%20wxEVT%20KILL%20FOCUS%20under%20Microsoft%20Windows

PurgeBlobs was faulty, but it was never having anything to purge. Fixed.

Fixed repetitive freezing of IDE when connection drops.
when connection lost error was beeing displayed, the involved wxYield
was calling pending plc status periodic update, itself trying to use connector.
At that time connector is still not destroyed and connection
is attempted again when calling GetPLCStatus.
=> Hack : Ensure connector is destroyed before reporting error.

Better error handling when blob transfer fail

Removed dead code.

Now expects 1 more columns in VARIABLE.CSV file generated by MatIEC. Pair with MatIEC commit 9cb7c8bf7dbc :
Add a column to VARIABLES.CSV, containing variable (derived) type name, additionally to current last column contyaining base type name

Merged workaround for loading bug happening after automatic resize of function blocks. It appears that some code in GraphicCommons.py loop endlessly when wires coordinate do not align with x or y axis. Those erroneous coordinate are now filtered out when loaded in the view.

Removed debug code and closed branch

GraphicCommons.py : Wire.SetPoints() move filtering before computation of Start and End points to avoid setting them with arbitrary directions.

GraphicCommons.py : rewrote Wire.Setpoints.
- trying to make it fix diagonal wires,
- wasn't clear what was intended before, so made it clear :
- duplicate point removal
- segment merging (only if asked)
- remove corners made of opposite direction segments

'Change POU Type To' becomes 'Duplicate as...', avoiding side effects of type change when POU is already instanciated. Also remove leftover returType tag in ex-function POUs, triggering exceptions at build time.

Fix PLCObject's purge failing silently with extra_files.