Adding item serialization/deserialization tests.

Closes #71
Clean java warnings on DataManager tests.

Some of the data manager tests had warnings and include errors from previous merges. Resolving and cleaning all of these.
Requests from last night:
- Implemented "isFavorited()" check on QuestionItem
- Implemented "haveUpvoted()" check on AuthoredTextItem
- Added "upvote(<item>)" call on QAController
Merge pull request #135 from Mobius5150/serializationtests

Adding item serialization/deserialization tests.
Merge pull request #138 from Mobius5150/cleantests

Clean java warnings on DataManager tests.
Fixed upvote() to correctly generate UniqueIds for upvotes, preventing duplicate upvotes from a given user on a given post.
Merge pull request #140 from stravant/master

Requests from last night