subuser 7.x-2.0-alpha2

What works:
- Creating subusers: configurable based on permissions what roles can create and what roles of users they can create.
- Switching users.
- Optional to storage of relation.
- Relations stored using relation.
- Editing and deleting (canceling) subusers.

What does not:
- Upgrade path from 6.x-1.x.
- Block/Unblocking subusers.
- Limiting number of subusers.

2faa4a2 Goto 'user' when switching to subuser and 'user/#/subuser' when returning.
be5dde6 Provide 'switch to user' user_operation.
e91edac update code comments and rearrange code.
b348387 Cleanup hook_permission() in subuser_switch.
799d995 Take advantage of views_bulk_operations.
d8d6c31 Move the ability to switch to a subuser to a sub-module.
bedfa1a Do not bother to support relation and views being optional since that usecase really just requires user/enitiy access API.

See #1145350: Finish 7.x-2.x port.