Use promises in storage module

[mirkoperillo]

At the moment the storage module uses callbacks.

Move to promises.

Storage module uses library localforage to persist data. Now Resting uses localforage.nopromises.min, move to the new version that supports promises.

Ref to code https://github.com/mirkoperillo/resting/blob/f3df3c23238468925c5b1412eab1534f76b08814/src/js/app/storage.js#L20