Scripts should check if a release exists before adding

[kmr2319]

Reference MB release: https://musicbrainz.org/release-group/a2babfd0-edb6-4355-93cf-67af81f92442

This was created via the script despite 2 other releases already existing for this album.

The original release from Dec-2018: https://musicbrainz.org/release-group/6a584035-7586-4be5-9ae6-848404ceeabb

A manually created release from about 2 weeks ago: https://musicbrainz.org/release-group/e2559cc4-d995-495d-a682-5d4250dd65d2

A check should be added to find an existing release before adding - this would avoid duplicate releases that need to be merged within MB.