[WIP] improve database performance and reliability

Summary:
let database test addOneTrackWithoutAlbumArtist have a file database

let the numeric unique id starts at 1 instead of 2

let fix warnings from QtCreator in database tests

DatabaseInterface: does not emit track changed signals for newly added

album artist name is directly a foreign key in Albums

should help to ensure greater reliability

lists of authors where not working so let's scrap this

use the unique fields of Albums for foreign key in Tracks

remove TracksArtists Table

no longer store tracks count and single disc states in albums table

Test Plan: tests are OK and Elisa application is still working

Reviewers: astippich, januz

Differential Revision: https://phabricator.kde.org/D16302