Merge pull request #53 from Gaerzi/master

Sync with my fork.
Fixed 'New Map' sometimes not loading valid map names
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Don't recreate sfml renderwindow if sfml version is 2.0 or lower
Update CodeLite project
Set default depth buffer size back to 16, added cvar gl_depth_buffer_size to control it