New title screen!

The title screen background is now composed
of two images. game_title_background is
scaled to fill the screen, while game_title
is scaled to fit in the screen while preserving
aspect ratio and aligned into the middle.


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56442 75b3775d-3801-0410-9e12-e2e43121521d