Summary:
The name of networks should be unique.
Also adds support for exact-name queries for AlamanacNetworks.
Test Plan: Applied migration with existing duplicates, saw networks renamed, attempted to add duplicates, got a nice error message.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin, PHID-OPKG-gm6ozazyms6q6i22gyam
Differential Revision: https://secure.phabricator.com/D19379
