LyX file format to 318. The Embedded files panel of document settings has
been simplied, with working add and remove buttons. Note that bease BufferParams
lacks buffer path information, extraEmbeddedFiles are vector<string>, instead
of EmbeddedFileList (as previously planned).
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@23606 a592a061-630c-0410-9148-cb99ea01b6c8