Bazooka/Grende training: Hide mission panel on pressing attack key

Update server dependencies in INSTALL.md

Clarify/rewrite a few OutError messages

Fix frontend showing 2 errors on engine fatal error (exit code 52) The exit code checked in the frontend was a hardcoded 2, which was outdated.

Clarify the wording of a few checkFails messages

Propagate fatal errors to OutError if checkFails called

Add hidden bazooka training achievement for 100% accuracy

Standardize hidden mission achievement in new Lua library "Achievements"

Add proper exit codes when halt-ing hwengine due to error

Fix cursor teleporting to center after leaving game with video recording

Whoops. Syntax error in uVideoRec

Fix video recorder not working if sound disabled (fixes bug #200)

Add variable to make state of sound system clear

Fix hwengine crash when using >1 controllers Reason: Data type mismatch for SDL_JoystickName, we wed in an index, but it expected a controller handle. Solution: Switch to SDL_JoystickNameForIndex.

Always use SDL_Map(A)RGB in SDL_FillRect for color This practice is recommended by official SDL docs.