Some improvements to the GP editor:
    - GP are now classified into groups, just like tracks: standard, user defined, and add-ons
    - allow empty GPs to be loaded by the GP manager, so that they can appear
      on the GP editor (but not on the track selection screen)
    - enable/disable buttons depending on the available options
    - provide some feedback after pushing the "save" button
    - some minor bug corrections and improvements
Drop support for GL 3.1  on windows

Fixed pipeline will be used instead
Add a dtor to animated mesh
Use __linux__  macro
Block event for one-element ribbon widget in the same way as multi-element widget.

This fixes problem with pressing left and right arrow in track and GP info screen.
Filtering actions is not needed now
Delete sync object
Fix second texcoord in instanced_object_pass.vert
Fix snb on linux
Fixed compilation of font_tool.
Set texture matrix in updateNoGL and not in updateGL
Do not use kart position if there is no kart
Do not allow specvalue to be below 0.

Just in case it shouldnt be possible anyway.
Tweak fade-in/fade-out times in cutscenes and remove hardcoded values
Merge branch 'master' of https://github.com/supertuxkart/stk-code
Fix negative value inside tonemap

It should be checked before but since it's not always reproducible.
kart selection screen : don't reload RTT scene if the selected kart hasn't changed
Merge branch 'master' of github.com:supertuxkart/stk-code
Try to include glew in stk.
Build a static version of glew.