Code re-organization and comments
Clean up the constructor regex and a bit more code reorganization

Put just the Rails engine require in a conditional instead of the
entire file. This will make testing easier when I actually write some :)
Revert back to more greedy constructor regex
Minor comment & code quality improvements
More comments
Use max z-index for box positioning
No longer necessary to use JSONP when opening files
Show the file extension on layous in Xray bar