session support that
* handle recent opened files (previously lastfile)
* save/load bookmarks when quit lyx
* save/load buffer cursor location whan a file is closed
* save/load windows position and size when a file is closed
* add rc entries load_session, use_lastfilepos,
screen_geometry_height, screen_geometry_width,
screen_geometry_xysaved.
* trigger LFUN_QUIT when Alt-F4 or close-button is used to close lyx.
* remove lastfile.h lastfile.C (merged in session.h, session.C)
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@13561 a592a061-630c-0410-9148-cb99ea01b6c8