Implement access to thesession.org API

[MatthewDorner]

thesession.org has one of the largest collections of ABC tunes and provides a web API. The app should allow users to access this API. I imagine it as a "special" Collection in the Browser, like "All Collections", something like "thesession.org (remote)". Then it would use a modified CollectionBrowser component that queries the API instead of the database.

The same search and filter options should be able to work, and users should be able to save tunes from the API into one of their own Collections.