Extracted ISerializationService

- Removed Serialize() method from all IMedia derived types.
- Created generic SerializeCollection(), SerializeItem(), Deserialize()
methods in ISerializationService class so serialization can easily be
mocked in unit tests.
- MediaList is no longer abstract. Reworked the serialized file path
property so that derived classes define their own FileName. Serialize()
and Deserialize() are now a wrapper around ISerializationService so it
can be easily mocked.
- Added a ton of unit tests.
- All of this in prep for adding fav/worst movie feature since I needed
a way of specifying the path to the serialized file instead of
MovieList/MediaList hard defining it. Also to increase unit test
coverage.
Partial implementation of movie rankings

- Added a view and viewmodel for movie rankings.
- View bindings currently not working since MovieViewModel creates the
MovieRankingsViewModel.
- Added MovieRankingsList as a derived type of MovieList so a new
FileName could be specified and extra ranking-specific methods added.
Removed SerializationService from constructor parameters

- Made SerializationService a public property of most classes so a
substituted object can be used for unit testing. Removed it as a
constructor parameter because MVVM Light doesn't like DI +
ViewModelLocator.
Movie Rankings

- Clicking on a movie now displays its information (poster, title, year,
RT view, plot, etc).
- Fixed a bug in Movie class where a null release date would blow
everything up.
- Added an event to command binding so that when the movie rankings
expander is clicked, a new MovieRankingsViewModel object is created to
refresh the data.
#21: fixed a bug with deleting a movie

- Fixed a bug where deleting a movie and then reserializing the list
would only serialize the SelectedYear's movies.
Added BackupService class

- Extracted backup code into a new class
Fixed MovieRankingsViewModel bindings

- Moved GetMovies() into constructor so the UI elements will be
populated when the VM registered with the IoC VM locator.
- Replaced backup code in MainViewModel with the proper class.
Merge pull request #26 from bretthysuik/favMoviesList

Merging favourite movie list feature into master branch