Implemented Automatic Versioning in Build Script

1. Changed build.gradle so that it edits the version numbers in
mod_pocketDim.java and mcmod.info.
2. Changed mod_pocketDim to use a placeholder for its version number and
fixed an annotation that was wrong. It would cause our mod_pocketDim
instance to not initialize properly. I removed what seemed to be
workarounds that were hiding the problem.
3. Fixed space in TileEntityDimDoor.invalidate() and corrected a
non-static access to a static field in mod_pocketDim.
4. Changed mcmod.info so that it users placeholders for the mod version
and MC version values.