Added Locale Service. Minor Controller Refactoring.

Hi there!

I started extracting some "buisiness" logic into a seperate provider/service. My goal, also in preparation for angular 2.0 some day, is to have as much of non binding logic to fit in services. So the migration won't be to much of a pain one day.

I started with this small chunk because it was just easy to extract. So that the monster SyncthingController can shrink in size over time.

Regards,
Dennis
I think this entire matching algorithm is unnecessary (my misunderstanding), and we really only need to do an equality check. The idea was to serve "en" if the browser only requested "en-US", but from what I understand now the browser should always send `["en-US", "en"]` in that case unless badly misconfigured. Anyway, just something that struck me, I can fix that later unless you want to gut it now. :)