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.

IDE: Fix one more sequel of wxPython4 port : typo in editors/TextViewer.py

Tests: Add a Makefile variable to allow changing standalone headless X server command (Xvfb by default)

Merge default head that was only merged in wxPython4

merged default

Add Docker image definition as reference platform to run IDE tests.

Tests: added tests/Makefile and a first test in tests/ide_tests. Test requires sikuli and Xvfb or Xnest.

IDE: Add -l or --log command line parameter to give a file where all content witten to console window will be appended. File can be /dev/stdout.