fixes #3697, #3701 - more comprehensive field validations

Fixes #4032 - Use object.id for comparisons

fixes #4152 - fix syntax error in _form.html.erb for hosts and hostgroups

fixes #3955 - added param_true? and snippet_if_exist template methods

fixes #3909 - add disassociate and bulk action disassociate to interface

fixes #3828 - set language locale for API messages and error responses

fixes #3826: no more sql errors when trying to search for environments (also domains, operatingsystems, and models)

fixes #3925 - create apipie param_groups for API v2 to DRY documentation

fixes #3920 - prevent 500 ScopedSearch errors on the API, raise UI errors correctly

fixes #359 - hostname spoofing for unattended installation templates