Code cleanup - Refactor utils.get_services()

Clean up utils.get_services.

This requires latest pynag.
Refactor and code clean up in adagios.status.utils

The code cleanup is not done yet, there is still a big mess but situation is better now.

* Refactor get_services()
* Refactor get_hosts()
* Use constants instead of magic strings wherever possible
* Add a bunch of unit tests for the refactored functions
* Taking advantage of latest LivestatusQuery (so update pynag)
Make unhandled hosts/services configurable

This patch moves the definition of unhandled/open problems
into settings.py

As a side effect of this, definition of unhandled can be overwritten
in adagios.conf by adding these to the config file:

UNHANDLED_SERVICES = {
    'state__isnot': 0,
    'acknowledged': 0,
    'scheduled_downtime_depth': 0,
    'host_state': 0,
    'host_scheduled_downtime_depth': 0,
    'host_acknowledged': 0,
}
UNHANDLED_HOSTS = {
    'state': 1,
    'acknowledged': 0,
    'scheduled_downtime_depth': 0
}

This partially fixes #471 although we are not providing the ability
yet to configure this from the settings web interface.
Merge pull request #477 from opinkerfi/feature-unhandled-is-configurable

Make unhandled hosts/services configurable
Merge pull request #475 from opinkerfi/cleanup-utils_get_xxx

Code cleanup - Refactor utils.get_services()