UX: require confirmation of revoking permissions on
repos/user groups/repo groups. We don't want people to
click on this accidentally.

UserGroup on UserGroup permissions implementation.
- user group can have another usergroup assigned
- it's impossible to assign usergroup on the same usergroup

consistent handling of grant/revoke of permissions widgets
- use 1 method for users and for users groups
- use common JS for ajax revoke
- cleanup code

- Manage User’s Groups: create, delete, rename, add/remove users inside.
by user group admin.
In this case, a user's group can be owned by several people thru an owner user's group.

Some refactoring of naming, permission handling logic.
- remove some code duplicity as well as inconsistent naming

further cleanup of UsersGroup

Renaming some names ... but trying not to change API or database scheme.

"Users groups" is grammatically incorrect English - rename to "user groups"

- and same story with "repositories groups"

This will only change the user facing texts. Names of files, modules, functions
and variables should be changed too.

Permissions on group can be set in recursive mode setting defined permission to all children
- more explicit permissions
- fixes for empty values in permission form

Autocomplete fixes
- use translation MAP
- move translation to top level in order to be used inside rhodecode.js
- re-use user and groups data in changesets page

#227 Initial version of repository groups permissions system
- implemented none/read/write/admin permissions for groups
- wrote more tests for permissions, and new permissions groups
- a lot of code garden, splitted logic into proper models
- permissions on groups doesn't propagate yet to repositories
- deprecated some methods on api for managing permissions on
repositories for users, and users groups