Invalidate the store at logout, emptying cached items such as artists,
albums and songs and then preventing them from quickly reappearing when
reconnecting with the same or a different account.
Closes#5.
* Keep track of pagination in the store
* Use Immutable in reducers
* Finish i18n, every available strings are now translated in English and French
* Add a loading indicator
* Premises of API error handling
* Better locale negotiation
