Load metadata.json from resources on DB reset.

This will ensure that a new (or upgraded) keyboard instance will know which
dictionaries are available for download so it requests missing dictionaries.
In addition, we increment the database version number to ensure upgrades of
existing Fava instances start with a clean slate.

Bug 22069694.

Change-Id: Id71310412682543a3931f9c5c03cb0369fa7b9ac