Reorganize network docs
Reorganize network docs

This change organizes the network docs by topic rather than letting
autodoc organize methods by the order they appear in the _proxy.py file.

Change-Id: I6366911a8410b43a567ca0d9afc22994639c80c8

dtroyer/python-openstacksdk,briancurtin/python-openstacksdk,briancurtin/python-openstacksdk,openstack/python-openstacksdk,dtroyer/python-openstacksdk,openstack/python-openstacksdk,stackforge/python-openstacksdk,stackforge/python-openstacksdk