SVGHMI: rename veriables in parse_labels.ysl2 for better readability

OPC-US client: add support for x509 and user+password authentication.

Commit for backup not including tests since encrypted OPC-UA test are still not valid.

IDE: fix wxPython 3->4 API change leading to exception in type selection menu in CodeFileEditor

OPC-UA, IDE: add CTN parameters to support OPC-UA encryption and authentication.

xmlclass had to be enhanced to support elements with no content in xsd:choice

IDE: Fix tooltip not being shown anymore on any toolbars since switch to wxPython4.

Cleanup and update version.py

IDE: Fixed About dialog exception on Windows, and typo in about dialog's content.

runtime: fix bugs introduced in previous commit, and refactor some code

Runtime: wx.app.mainLoop and twisted reactor now share main thread with runtime.Worker.

This fixes exception when invoking python interactive shell from Runtime's tray
icon right-click menu.

Probably a consequence of wxPython upgrade, together with initial bad idea to
move wx.app.mainloop in non-main thread.

Remove useless assignment

SVGHMI: update generated XSLT

tests: fix load_and_build_tests.pytest

Leftover import from previously commented-out tests. Commented out as well.

Merge changes from default in wxPython4

SVGHMI: add support for multiline widget declaration using svg:desc.

Declaration started in inkscape:label and interupted by a '\' can be continued in the description field.
After an empty line, the rest of the description field is left for description text.

Runtime: Fix PLC python thread crash in case of exception in PostStart customization hook.

IDE+Runtime: fix exception when reconnecting with non-empty trace/force list.

Sometimes, remote call to SetTraceVariableList returned None just after reconnecting:
- changed caller to accept None (in case of connection problem)
- changer SetTraceVariable list to return 4 (DEBUG_SUSPENDED) if debug is suspended