Offline Unit Tests: DataUploadService

* Creates and injects `OAuthRequestFactory` for generating requests.
* Injects `TestOAuthRequestFactory` in unit test environment to generate mock requests.
* Fixes test `shouldGenerateGPX_shouldSubmit()` (previously failing) for offline execution.
* Prevents actual requests from being sent over the network while running tests.
* Prevents `UnknownHostException`s from being thrown by background threads.
Merge pull request #205 from mapzen/chuck/offline-unit-tests

Offline Unit Tests: DataUploadService