Fix the Model Relationship

[lisa-fehr]

The original database isn't Laravel friendly.

I never ended up tagging an image with more than one tag.
uber_tags should have a direct relationship to uber_gallery. No more uber_tag_assoc silliness.

• Make a migration to add tag_id to the uber_gallery table
• Make a migration to move the tag associations from the uber_tag_assoc table
• Fix the tag relationship on App\Models\UberGallery by using the tag_id column
• Remove App\Models\UberTagAssoc
• Add a migration to remove the uber_tag_assoc table