graphics/text/.gitignore additions
dist: Add Desktop Entry files for all three IWADs

These are intended to be useful for packagers for distributions of
GNU/Linux, *BSDs, illumos, and any other operating system where they
may be relevant.  Hopefully without the need to edit them :)

This is part of the goal of issue #100 to ease distributions' support
for showcasing Freedoom.
dist: Add some AppData XML files

Based on the AppData that the Fedora Project wrote for their
distribution, here's three separate ones for each of the IWADs.

This is the second major part of completing the goal in issue #100