[WIP] Update to Gitbase v0.20.0
Closes #424.
Marked as WIP as waiting for final Gitbase v0.20.0 release.
This PR removes the MysqlCli component and uses the MySql client provided by Gitbase itself.
The tests are failing due to a bug that will be fixed by #432.
Looks good so far. But it looks like there are more test that are failing, not only because of #432.
@carlosms thanks I didn't notice. To simplify review I've just rebased to master to solve conflicts, gonna address the tests now and also update to beta3.
Rebased on master and updated to use gitbase-v0.20.0-beta4.
Updated to gitbase-v0.20.0-rc1.