[feature] Auto update databases

[sync-by-unito[bot]]

Only after ‘Remember default melody settings over database update’ #73 and #174 .

┆Issue is synchronized with this Trello card by Unito ┆Attachments: https://trello.com/c/ByMMVAZ4/87-remember-default-melody-settings-over-database-update

[sampie777]

Some requirements:

• user should be able to toggle this feature off
• auto update should happen with a specified interval, e.g. not more than once a week or month. Maybe this could also be set by the user?

[sampie777]

A way to do the update checking: Send a list with the uuid's of all local song bundles to the server. The server responds with the current hash for each of these ID's. If a hash doesn't match, that bundle needs to update.

More mobile data can be saved by hashing the returned array of hashes in the same order the uuid's were sent.

[sampie777]

Or just let the server return a list of UUID -> hash maps of ALL bundles.

Let's start with the server returning all bundles. Later we can implement a filter send by the client to reduce this list's length.

The list should include UUID and hash:

[
   {"uuid": "", "hash": ""},
   ....
]