Supporting pagination in api v2.0

Implements bp support-pagination-in-api-v2.0

Add sort and pagination feature for api v2.0.
*Add sort_key, sort_dir for sorting feature.
*Add limit, marker, page_reverse for pagination feature.
*Add emulated sorting and pagination

Native pagination and native sorting implemented for:
*plugins: ovs, linuxbridge
*extensions: l3 securitygroup

Emulated pagination and sorting enabled for:
extensions: lbaas

Change-Id: I28ec6ab7bcae9839cb42c6d60bbfff7250de13ed
Merge "Supporting pagination in api v2.0"