Allow querying org types by name

This is case insensitive because we didn't want the case where we ended
up with different org types purely based on the case of their names.
Filter org nodes by name and abbreviation

If both parameters are given they AND not OR. We have chosen to make the
queries case insensitive so we don't end up with nodes differing by
case.
Merge pull request #201 from alphagov/organisation-querying

Organisation querying