pynag.Parsers.LivestatusQuery new features

Changes in LivestatusQuery:
* Support for new __gt and __lt suffices
* __eq__ implemented for LivestatusQuery
* Change create_filter_statement so that it accepts list instead of arbritrary arguments
* New method: add_filter() for adding a single filter
* New method add_or_statement()

Changes in Livestatus:
* Livestatus.query() simplified by moving pre-proccessing into a seperate method
* Livestatus.query() simplified by moving post-processing into a seperate method