[FEATURE][!!!] Support for signals

Signals are available since TYPO3 6.x:

- User has been imported
      Class: tx_igldapssoauth_typo3_user
      Name:  userAdded
- User has been updated
      Class: tx_igldapssoauth_typo3_user
      Name:  userUpdated
- Users have been deactivated
      Class: tx_igldapssoauth_scheduler_synchroniseusers
      Name:  usersDeactivated
- Group has been imported
      Class: tx_igldapssoauth_typo3_group
      Name:  groupAdded
- Group has been updated
      Class: tx_igldapssoauth_typo3_group
      Name:  groupUpdated
- Authentication failed
      Class: tx_igldapssoauth_sv1
      Name:  authenticationFailed

In addition, hooks processUpdateUser and processUpdateGroup have been
deprecated in TYPO3 6.x.

Resolves: #61003
Change-Id: I4debb49d0f4496adf2d01e3ff5b540e2a2d26204
Reviewed-on: http://review.typo3.org/32201
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>