Ignore compiled game logic (game, cgame, and ui)
Import some 2D graphics and shader files from Turtle Arena

There have been some changes from Turtle Arena for q3 compatiblity, but still more to be done.
Import common textures from Turtle Arena
Add background placeholder
Import some missing UI gaphics

From Turtle Arena's base_ioq3ztm.
Remove Turtle Arena randombot icon source
Import skirmish menu button

From Turtle Arena's base_ioq3ztm
Remade addbotframe and cut_frame as SVG
Remade frame1_l, frame1_r, and frame2_l as 4x SVG
Revert "Import skirmish menu button"

This reverts commit 4d2a7c9c5f27d0faf1679279b7357ac0e88369c2.
Make slider button fit Q3 colors

Moved orange _1 file to _0 and made _1 yellow.
Add placeholder arenas.txt and bots.txt
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'