Source for local forage

Local forage (https://github.com/mozilla/localForage) is a wrapper library for client side databases. The API is pretty similar to local storage. If supported, it will use the indexedDB/webSQL of the browser. It might be an alternative for use cases, where not all the flexibility of indexedDB is required, so I think both sources have their right to exist. 

This is work in progress, feedback is welcome!

Todo:
- refactoring of the local forage tests, because the tests use basically just a copy of the local storage tests (localforage is configured in this case to just use localstorage). What would be the best way to refactor these tests?
- maybe support customization of drivers