REGISTRAR, RPC: added new init method for new registrar gui

- New method will load almost everything in one call into
  registrar to determine and display current state
  (e.g. user is already member, can/can't extend membership etc.).

  It won't be used by old registrar gui !

- Added new AlreadyRegisteredException thrown when user is
  member of vo/group and tries to get initial application.
REGISTRAR: catch also MemberNotExistsException

- When retrieving data for initRegistrar() catch MemberNotExistsException
  for extension app form, since it's correct minor exception.
Merge pull request #547 from zlamalp/registrar

REGISTRAR, RPC: added new init method for new registrar gui