Improve performance of TextClass type objects by making BaseClassList and DocumentCla...

Improve performance of TextClass type objects by making BaseClassList and DocumentClassBundle containers of pointers rather than of objects, thus reducing the need to copy. Since these classes are singletons that live the life of the process, there's not much need to worry about memory leaks.

We take the opportunity to make TextClass objects noncopyable, nonassignable, etc.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@23526 a592a061-630c-0410-9148-cb99ea01b6c8