try pulling OpenAL and SDL Windows libraries from mirrors
added in-game SHP viewer with frame slider
added the game asset viewer to d2k mod
remove duplicate ra-desert bridge tiles
added .mix file support for game asset browser
added button to extract the selected SHP and convert it to PNG
add a dump everything to PNG options for @xanax
fix Makefile

OpenRA.Mods.RA.dll now depends on the Utility.exe
added MinimumThumbSize to ScrollPanelWidget

closes #2865
game asset browser UI polishing

- display file extension
- show total frame count
- dark background for preview
wire up the import from PNG to SHP button

store everything in user directory to not junk up the game
and for file permissions on Mac/Linux when installed
adapt asset browser for R8 files
Adjusting infantry run animations to speed

I noticed that by default the run and prone-run animations are way too fast for the infantry movement speed. I used Tick values to fix this, taking into account individual speed. I used Tick: 80 for Speed: 5, 100 for speed 4 and 120 for speed 3. Some fine-tuning may be needed, but it already looks much better than before.
Merge pull request #3291 from reaperrr/patch-2

Adjusting infantry run animations to speed
Add unit guarding
Merge pull request #3281 from Mailaender/sdl-openal-mirrors

Added OpenAL and SDL Windows dependency DLLs to mirrors
Merge pull request #3192 from Mailaender/asset-browser

Created an Asset Browser to view and convert Sprites
Merge pull request #3233 from ScottNZ/follow

Add unit following/guarding
Move Renderable into its own file.
Make the guts of Renderable private.