fixes #3826: no more sql errors when trying to search for environments (also domains, operatingsystems, and models)
fixes #4115 - added missing LICENSE file
fixes #3828 - set language locale for API messages and error responses
fixes #3909 - add disassociate and bulk action disassociate to interface
fixes #3955 - added param_true? and snippet_if_exist template methods
fixes #4152 - fix syntax error in _form.html.erb for hosts and hostgroups
Usergroup roles support

Working version which currently breaks a lot of tests however is ready
for testing by devs. There are still things to improve. Also we enable
users that can edit usergroups a privilege escalation atm.
Fixed tests
Add cycle detection and prevention in usergroups
Add migration for caching existing user roles
Fixed issue for redundant structures
Recache after remove

The only way to keep correct cache without complete recalculation or
having complete paths stored
With this we don't even need user_membership caching
Usergroup membership caching
Admin flag can be assigned to usergroup
Small refactorings
Roles design
Reviews
CRUD for filters
Add taxonomies to filters