Fixed compile errors on IntelliJ 14 EAP

Hey Urs,

_Feel free to abandon this pull request if you already were working on this locally or if I did it wrong. I'm only sending this in case it can save you a few minutes of time._

I recently downloaded the IDEA 14 EAP and your gerrit plugin failed to load on it. Therefore, I forked your project and cleaned up the compile errors.

There really wasn't that much that changed, actually:
* `GitHttpAuthDataProvider` moved into a new package
* `GitHttpAuthDataProvider` added a new method to its interface, `forgetPassword`
* `UntrackedFilesNotifier.notifyUntrackedFilesOverwrittenBy` changed its API

I guessed at what should be done to fix it, but I'm not sure if I did it the right way, or even how to cause the code to run those lines so I could make sure they wouldn't explode, but I thought I'd put it out there for review anyway, and you could either take over at this point or you can advise me how to rewrite this.

Finally, I based this branch off of intellij13, but of course, you'd want to pull these changes into a new intellij14 branch. Not sure if github makes it easy to do that or not...