Support pagination for ceilometer APIs

This spec aims to add support to the listing APIs call for limit,
marker, and sort_dir(sorted by timestamp) and groupby(especially
by event types) filters

Implements: blueprint ceilometer-events-pagination
Change-Id: I4bac0a5e4b8fc771fb10c66cf710a005d9808e71
Merge "Support pagination for ceilometer APIs"