Slight StationFinderCtrl cleanup

- Else block(instead of early return) in findStation
- Actual usage of the error message stationFinder returns
Moved loading state to stationFinder service

Also:
- stationFinder service now using .factory
- Rearranged tests
Moved stationFinder error message test
Moved bestStation storage to stationFinder, updated tests
Merge pull request #17 from csampson/issue-12

Issue 12