This is the last of a series of patches that merges the layout modules development...

This is the last of a series of patches that merges the layout modules development in personal/branches/rgheck back into the tree.

Design goal: Allow the use of layout "modules", which are to LaTeX packages as layout files are to LaTeX document classes. Thus, one could have a module that defined certain character styles, environments, commands, or what have you, and include it in various documents, each of which uses a different document class, without having to modify the layout files themselves. For example, a theorems.module could be used with article.layout to provide support for theorem-type environments, without having to modify article.layout itself, and the same module could be used with book.layout, etc.

This patch adds the GUI for managing modules.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@20282 a592a061-630c-0410-9148-cb99ea01b6c8