Better fix for bug 3510 (by me, Juergen, and Jean-Marc)

Better fix for bug 3510 (by me, Juergen, and Jean-Marc)

	* lib/layouts/IEEEtran.layout: Add a proper definition to the
	preamble when using the MarkBoth environment (fix bug 3510).
	Allow inserting an optional argument for theorem like environments.
	Remove white space from begin of line in preamble stuff.

	* lib/templates/IEEEtran.lyx: Reintroduce the MarkBoth environment
	in the document body thanks to the fix above. Use optional argument
	instead of ERT in Theorem environment. Use the new --Separator--
	environment for splitting biography environments.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@18767 a592a061-630c-0410-9148-cb99ea01b6c8