[v7r2] scriptdocs

[TaykYoku]

This PR provide some #4853 and #4954 changes.
Much of the description of scripts from CommandReference *.rst's are transferred to the __doc__'s of a script files.

The main change in LocalConfiguration.py and Script files, other changes concern the design of script docs mainly.

BEGINRELEASENOTES

*All systems affected:
CHANGE: use __doc__ for script help message, remove filecfg as argument from usage description

*Core:
CHANGE: when import Script, a help message is formed from __doc__, not need to use Script.setUsageMessage(__doc__)

*Configuration:
CHANGE: setUsageMessage in LocalConfiguration will parse received str value for building help message

ENDRELEASENOTES

[fstagni]

This looks fine to me, with just a small caveat: for the dirac-version and dirac-platfom script can you align to what I have done in #4954 ? To avoid possible conflicts.