removed presence validation on master_version_id
Merge pull request #39 from dhouk24/update_repo_and_version_schemas

removed presence validation on master_version_id
implements tags (models, migrations, tests, views)
removed repositories#index
creates repo show page, shows tags on repo
add tags on new repo form
Merge pull request #40 from dhouk24/implement_version_tags

Implement repo tags
creates version history route, action, view
removed erroneous JS line
Merge pull request #42 from dhouk24/show_version_lineage

Show version lineage
fixes merge conflict