First patch for auto-cls-layout feature, from Bo Peng (ben.bob@gmail.com)

First patch for auto-cls-layout feature, from Bo Peng (ben.bob@gmail.com)
	layout file in the same directory as .lyx file will be used. .cls can also
	be in this directory.
	* src/buffer.C, bufferparams.C: move filepath to bufferparams so this
		info will be available in getToken()
	* src/lyxtextclasslist.h, .C: add addTextClass() that read a .layout file
		from filepath.
	* src/lyxtextclass.h, .C: pass filepath to LyXTextClass::load(). .layout
		file in filepath will be loaded before system ones.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@13611 a592a061-630c-0410-9148-cb99ea01b6c8