CORE,GUI,REGISTRAR: fixed identity consolidation behavior

CORE:

- Unified ext source names in internal sessions to "INTERNAL",
  they contained ext source type in name before.

  This doesn't affect authorization, since it's based on actor
  (for service roles) and on ext source type for non-authz access.

  Ext source 501 should be deleted, since it's not used for any user
  and now shouldn't be used by any component or internal session.

GUI:

- When searching for similar users, use Identity instead of RichUser
  in order to keep private data private.
- Fixed return parameter of identity consolidator link (target -> target_url).
- Prepared code for new consolidator (commented out).
- Use link of identity consolidator with proper users authz in notice to admins.
- Source format.

REGISTRAR:

- When searching for similar users, parse multiple-value email field
  and search by all emails.
- Do not return identities of service users when searching for similar.

DISPATCHER-NEW: 

- Update session in tests to EXTSOURCE_NAME_INTERNAL.