Use asyncStorage (indexedDB wrapper) instead of localStorage

[willyaranda]

localStorage is syncronous, so it blocks UI. You should use asyncStorage[1], which is a localStorage-like wrapper for indexedDB (so it's asynchronous).

[1] https://github.com/mozilla-b2g/gaia/blob/master/shared/js/async_storage.js

[aesedepece]

Shut up and take my money!!!
That would avoid the little UI freeze when entering a chat with lots of messages inside. It will be implemented ASAP :)

[aesedepece]

Fixed by commits 6f82fe3 and a9c97b5

In addition if it detects that there is data from a previous version of LOQUI, it imports the data.