Fixed issues with group renames for local repository group admins.

- revoke permission on yourself check was triggered thus preventing
group update. Moved this check into update permission function

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

follow Python conventions for boolean values

True and False might be singletons and the "default" values for "boolean"
expressions, but "all" values in Python has a boolean value and should be
evaluated as such. Checking with 'is True' and 'is False' is thus confusing,
error prone and unnessarily complex.

If we anywhere rely and nullable boolean fields from the database layer and
don't want the null value to be treated as False then we should check
explicitly for null with 'is None'.

better detection of deleting groups with subgroups inside.
Added less strict checks on delete group routing so we can delete zombie groups
(those that are not in filesystem but in DB)

"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.

Group management delegation:
this allows users to become an admin of groups
a group admin can manage a group, change it's name
or permissions. A group admin can create child group
only within a group he is an admin off.

Top-level group can be only created by super admins

Use common function for generation of grid data
- admin grid now has dedicated edit button, and uses changeset_cache
- some small improvements to grid
- all other datatables use this

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

sqlalchemy sessions cleanup in admin
Cleanup settings options

#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

Added handling of ignore whitespace flag in changesets
- fixed messages for FK validation

commit less models
- models don't do any commits(with few exceptions)
- all db transactions should be handled by higher level modules like controllers, celery tasks

unified generation of repo groups choices
added on-the-fly conversion to new repository groups format (supporting path as a link)

Added friendly message about removing a group that still contains subgroups.
Fixed option to remove a group that is not in filesystem (ex. someone deleted it intentionally on filesystem) in this case RhodeCode will simply just throw an error message saying this group cannot be deleted.

implements #226 repo groups available by path
fixes #259 Groups with the same name but with different parent group

fixes #200, rewrote the whole caching mechanism to get rid of such problems. Now cached instances are attached
to db repository instance, and then fetched from cache. Also made all current test work.

#47 added editing of groups, and moving them between. Added check constraint for groups
to prevent of loops

#47 implemented Adding of new repo_groups+forms+validators. Fixed sorting of repo groups by main names in multiple locations. Removed some unneeded calls to self.sa for exchange to .query() methods.
Added new db unique key for Group