Initial commit to add persistant user settings

This commit adds the 'rails-settings-cached' gem to the project Gemfile,
and contains files created from the generator `rails g settings Settings`.
There are no tests added, as there is nothing to test against.
Finished adding rails-settings-cached. Closes #5

This commit finishes adding rails-settings-cached related features.
This includes a new SettingsController, which offers JSON CRUD operations to the
persistant settings store, as well as a number of tests to verify functionality
of the controller and related routes.
Merge pull request #9 from spectra-music/features/user-preferences

Features/user preferences