Merged default's changes in wxPython4 branch

Tests: fix project edit test sikuli IDE test.

Background click based on bitmap matching doesn't work.
Grid dots are not good match candidates.
Rendering probably affected by virtual display's bpp or rasterizer approximations.

runtime, retain: remove forgotten debug code.

Runtime: removing dead code

IDE: removed one (last ?) wx.NewId() that was called on each opening of project tree popup menu

Tests: Re-introduced pytest based tests. Fixed them a bit, commented-out otherwise. Application tests only runs with logging test, and PLCOpenEditor tests seem broken.

Tests: Enhance robustness of stdout driven waiting state in Sikuli based tests.

Some tests were randomly passing, because from time to time waiting for idle was skiped. It was combination of multiple problems :
- buffering on stdout (now use readline + flush for each write to log)
- it is sometime required to wait for activity before waiting for timeout added "WaitForChangeAndIdle" to "stdoutIdleObserver"

Tests: add an IDE test that relies on image matching.

Tests: re-introduce xvfb+x11vnc target in Makefile : xvfb_sikuli

Fix sequel of wxPython 4 port : double click on tab wasn't maximizing and was showing exception.

Tests: Makefile's PIPESTATUS turned into small letters (wrong vim shortcut ?) leading to always passing tests.

Tests: Various enhancements in Makefile and sikuli common python code.

Tests: Added BEREMIZPYTHONPATH to point to Python interpreter to use for tests.

Documentation/comment fix.