Node.Index: support includes, count and filter by location
Vps.Index: filter by user
Maintenance: fix cluster unlock
Per-environment VPS configuration and config chains
Environment config per user, remove location_type, update VPS create

Environment config per user takes precedence over default environment
config. location_type is replaced by environment and its settings.

VPS creation works in two modes - admin and non-admin. Admins choose
node on which to create the VPS manually. Non-admins can choose
either an environment or a location. Best fitting node is then
selected from the chosen environment/location. Non-admins must comply
with the rules in environment config.
Maintainable: fix method maintenance_check!
Environment, OS template, User: list id, allow for non-admins
Resource Location: list for non-admins, includes and total count