First attempt at caching tangents meshes
Second try of my previous pull request, which was partially reverted due to caused crashes and memory leaks
Merge remote-tracking branch 'upstream/master'
This will (hopefully) solve the memory leaks in dynamic ribbons and image button widgets
Issue #1588

Fixed crashes in track info screen
Check texture cache before adding an icon button's disabled texture
Actually display secret achievements once they have been achieved.
Don't show a password entry field for the currently logged in user.
Added support for detecting BSD versions; added uname based fallback
on linux in case /etc/*release does not find valid info.
Remove data after "-" when using uname (which could theoretically be
used to identify a system).
Fixed windows compilation.
Change "Cancel" to 'Exit game' and make the back arrow invisible if
the login screen is shown before the race start.
Replaces sfx->getStatus with isPlaying() functi n which is faster
(for #1511).
Replaced more getStatus() functions.
Reverted 77bd4140a803088231191925e10e4a58e44e0828 (which caused
crash and other sfx to be played only once).
Merge remote-tracking branch 'upstream/master'
Started to let all sfx related command be executed from the sfx manager
to avoid race condition and crashes.
Use length limit for dynamic ribbon labels in the GP editor
Let all SFX commands be handled by the sfx manager thread (otherwise
events could be handled in the wrong order, e.g. a delete from the
main thread before the play in the manager thread, resulting in a crash).
Should fix #1511 and #1604.
Merge branch 'master' of https://github.com/marcoll/stk-code into marcoll-master