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.