MOD-68: Differentiate between Release Upload & New Module

I've included a couple fixes to help prevent people from uploading a new module when they are intending to upload a new release.

• the navigation link is now "Upload New Module", not "Upload"
• I wrote a controller that displays an alert on the upload page if the module being uploaded looks similar to one already in the system. ([screenshot](http://from.elliottwillia.ms/image/0m2u052U0s1a))