graphics: Rename title screen.

By popular vote[1] on Doomworld we are ditching the "Ultimate" name
for Freedoom 1; the two IWADs are now named "Freedoom: Phase 1" and
"Freedoom: Phase 2". Rework the title screen to incorporate the logo
from the menu, and add a matching logo for FreeDM.

[1] http://www.doomworld.com/vb/freedoom/66855-renaming