#145737 by yhager, documentation cleaned up by myself: add support for RTL CSS...

#145737 by yhager, documentation cleaned up by myself: add support for RTL CSS overrides and default RTL CSS override files for modules
Note: properties, which are different in the RTL display are marked with /* LTR */ in default CSS files now,
so maintainers remember that changing them should also have an effect on RTL CSS files.

This should open the way for better RTL (right-to-left written) language (such as Arabic and Hebrew) support.