Add tube rack delete action
Specs for tube rack delete action
Bump version to 1.8
Fix specs
Add requirement to delete tube rack action
Add constraint to avoid having a same tube in two tube racks
Remove label error specs (not this branch)
Merge pull request #41 from llh1/53886775_add_delete_tube_rack_action

53886775 add delete tube rack action
Use add_index with unique => true instead of add_unique_constraint (does not work properly)
Bump version to 1.8.1
Merge pull request #42 from llh1/54198226_fix_migrations_8_and_9

54198226 fix migrations 8 and 9