CORE: Fixed type of returned exception for LoA

- When creating member, check if he/she can be member by loa
  and VO membership expiration rules. If not, throw an exception 
  which will rollback creation.

- Skip creation of member on synchronization of group when
  we can't properly set membership expiration based on VO's rules.

- When member is checked for possible extension and fails,
  we must return INSUFFICIENTLOAFOREXTENSION type of exception,
  so GUI will perform redirect.

  There originally was INSUFFICIENTLOA which is case only when user
  is not yet member of VO.

- Added javadoc for methods canBeMemberInternal(), manageMembershipExpiration().