Merge pull request #75 from Gaerzi/master

Sync with my fork.
Merge pull request #76 from Gaerzi/master

Dat write
Merge pull request #77 from Gaerzi/master

Disk write
Clicking cancel when creating a new map will not open the map editor
We still need to at least draw the grid if the map is empty :P
Merge pull request #78 from Gaerzi/master

Sync with my fork.
Fixed possible crash on merging overlapping lines
Update project for debug build
Fixed rendering glitch when selection numbers were enabled with SFML
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Properly init map object variables on all constructors (sectors were being created with random types/tags)
Pasting things shows the correct sprite again
Merge pull request #79 from Gaerzi/master

Well, that's weird. They weren't in master already?
Merge pull request #80 from Gaerzi/master

WHAT IS HAPPENING?
Fix problem with using the up arrow key on the map editor in linux
Add some extra checks to GLTexture binding
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Don't show add button on map object property list when map format isn't UDMF
Merge branch 'master' of https://github.com/sirjuddington/SLADE