Fix and simplify par params parsing in get_containing_layout.

The previous verion did not catch \align <alignment>.

Richard, this should go to branch as well.
A stringstream is overkill here
Fix return value of CVS::toString() + cosmetics

CVS::toString() returns a docstring, so rather be explicit than relying on a
cast that not everybody understands how it works at first sight.
Remove heavy includes
Avoid implicit copy
tex2lyx: support for KOMA-script's \caption* commands

- To my knowledge tex2lyx supports now all caption constructs provided by LyX.
- InsetArgument is correct here, I therefore deleted the FIXME.
Honor paragraph parameters when converting chunk layouts.

Fixes: #9320.