Db refractor

[wiiznokes]

Refractor of the DB code to fix this issue #104 .

Now we retrieve all mime types, instead of just custom ones

There is also various improvement, like using buffered query for sql, and async read of pipe when reading clipboard content.
And the Db now implement a Trait, to make the code cleaner.

Todo:

• fix the search
• fix issue where the clipboard is not visible in the applet
• better solution for prefered mime type (make this a config option) and also use it for qr code