[ADD] test_workflow: added some tests for the workflows.
[DOC] workflows: started to write some workflow documentation.
[DOC] workflows: added Conditions section.
[IMP] workflows: added docstring, some variable renaming (to wkf_expr).
[DOC] workflows: added Signals section.
[DOC] workflows: improved Triggers section.
[DOC] workflows: added Flow start and flow stop section.
[DOC] workflows: added Subflow section.
[DOC] workflows: added remaining sections for the Activities.
[DOC] workflows: added Kinds section.
[ADD] workflows: added some tests.
[ADD] workflows: more tests.
[ADD] workflows: some split_mode tests.

I am not sure if the Workflow K is determinist though
so it could maybe end up in activity c instead of b
(and thus fail the tests).
[FIX] workflows: fixed the non-deterministic workflow K, added workflow L in tests.
[IMP] doc: improve workflow documentation
[FIX] avoid error message in the web client when we go on the Apps menu, replace it with a warning message explaining that the apps is not working currently
[DOC] workflows: typos, and removed inaccurate environment symbols.
[REM] workflows: removed temporary run.py script from the tests.
[MERGE] workflows: added some documentation and some tests.