Parsers/LivestatusQuery - More helper methods.

Added a few helper methods to LivestatusQuery and changed
__init__() so it no longer depends on pynag.Utils.grep_to_livestatus() internally.

This is part of a bigger change to refactor and clean up adagios.utils.get* methods and support cleaner bridge
between livestatus and querystrings.

This patch and a cleanup of adagios.utils.get_services() is required before
we can proberly support opinkerfi/adagios#470

Please review and give feedback.
I feel the name of this method is too generic as it doesn't imply that arguments ar Or-ed together. Don't really have a suggestion, maybe create_multivalue_filter_statement (it's bad) :)