Initial version of TraktV2 manager class with OAuth helpers.

- Added custom HTTP client using okhttp for use with Apache Oltu.
- As a consequence okhttp is not optional any longer.
Start development on 4.x.
Clearly separate endpoint from methods.
Add Shows `summary` method, tests, separate RestAdapter with auth.
Merge branch 'show-summary' into api-v2
Add Movies service, Movies summary method, tests.
Merge branch 'movies-summary' into api-v2
Refactor Shows tests, fix test show and movie.
Explicitly request JSON response body.

- Extract header constants to class constants.
Add movie and episode `checkin` method, tests.

- Ensured all entity values can be null (always use object variant for base types).
- Moved some BaseEntity properties up to Show and Movie.
Add token endpoint test.
Supply valid access token for testing.
Revert to using single `RestAdapter`.

- It should be up to the user to create separate instances without auth if so desired. Doing this at this lower level will run into issues fast, we also would have some issues with separating auth-required methods from others.
Support check-in deletion.
Support check in responses, including error response.
Merge branch 'checkin' into api-v2
Cancel the active checkin after testing checkin blocking.
Only add auth header if there is an access token set.
Add basic OAuth helper tests (ensure path + no scope).
Add docs to shows summary methods.