Fix for issue #529.

* replaced precondition with if-statement in class ChunkMeshInfo.
Merge branch 'develop' into monitoring
Merge branch 'develop' of https://github.com/MovingBlocks/Terasology into monitoring
Miniscule fix for missing space in single player ui.
Fix for issue #532.
Merge #530 by @mbrotz to fix #529
Added DoubleClickListener to module dialog.
 Double clicking toggles mod selection.
fixed core mod toggle bug.
More work for mod data extensions.

+ Added support for mod data extensions in mod manifest
+ Mods with mod data extensions will now register them in the mod data extension registry when the mod is enabled
Merge branch 'develop' of https://github.com/MovingBlocks/Terasology into stackable-chunks-2