Add some class factory function to ease declaration of simple POU libraries in customizations (i.e. TC6 XML file only, no special C code generation)

Small pep8 conformity enforcement.

Better have globals passed to python extensions (-e) than locals.

launcher : move call to ShowSplashScreen and BackgroundInitialization to PreStart()
It doesn't change behaviour of launcher in beremiz, but may have some impact on some customizations.
Some customizations need to squeeze some bitmap folder init in between app creation and ShowSplashScreen

modbus extension code cleanup, from smarteh's patch

Merged Mario's modbus branch. Fixed line endings.

merge

Ignore bug report files.

Add support for Modbus (TCP and RTU) working as master & slave

merge

fixed erro introduced 2 commits ago (-e) : tuples have no reverse() method

Trying to get better logging/display of exceptions at runtime's startup

Changed way to deal with extensions arguments (-e) so that path and filename are stored independently and accessible for extensions themselves.

Textviewer : moved call to Colourise in a better place, so that ST highlighting gets also updated when typing in some case, not only IL

Main runtime template C code : Added HAVE_RETAIN preprocessor definition for customized build to signal it provides IEC-61131 Retain memory handling function. Removed targets/Xenomai/plc_Xenomai_noretain.c, now useless.

Clarify licensing, and packaging of runtime only files :
- moved and split targets/typemapping.py into runtime/typemapping.py and runtime/loglevels.py
- added runtime_files.list pointing to files necessary for runtime, and referring to runtime license

Enforced check_source.sh pep8 and pylint rules.

runtime/WAMP: Fixed secret loading into configuration. Fixed secret commandline switch handling.

runtime/WAMP : was 'Added time print on session left.' from dporopat. Purpose is to log (dis/re)connection, to help debugging connection problem

runtime/Wamp : adapt to unicode being enforced in latest crossbar API. Updated some documentation, to explain why there is unused definitions like SubscribedEvents or DoOnJoin.

Extend python<->PLC global variable description "GlobalDesc" to support Initial value setting.

Rebased from dporopat change "add initial value to runtime.py file", which means :
- GlobalDesc is used by some customized beremiz python runtime
- Those runtimes need to know what is initial value of these special variables

update tests/wamp README file, based on changes from dporopat.

Fixed WAMP test (crossbar confile upgrade and use same ID on both PLC and IDE side)

Fixed changes from dporopat and agregorcic about WAMP CRA and config.