Fix custom keybinds not working
Disable testing keys when not in debug mode
Add 'Show Things' checkbox to map preview panel
Add basic version/update check

- Option to check for updates on startup
- Option to include beta versions in update check
- Menu item 'Help -> Check for Updates...'
Fix VersionCheck when no connection present
Fix potential crash in MapLine::needsTexture
Remove sides with invalid sector references on map load
Add map statistics to map preview panel
Add map size to stats line on map preview panel
Fix wrong 2d mode flat texture appearing after deleting a sector
+ use hard-coded temp directory (if available) during deployment image creation
Merge branch 'master' of https://github.com/sirjuddington/SLADE into osx