Fixes #4596 - Change parent of host group via AJAX

Reparenting host groups requires submitting the form to see the changes
nowadays, this fix makes the host group model inherit all properties
from the parent and show them in real time.
Fixes #7041: fixed incorrect belongs_to mappings

:conditions reference columns from the local (to the relation) table,
while the condition is applied to the remote side of the association.
The condition can be removed, as it's redundant anyway.
refs #6161 - Add test to make sure override is marked on create
fixes #7336 - editing compute resource should not clear existing attributes from the form
Fixes #6874: Integers in settings can be up to 8 digits to avoid bigint out of range error