Add support for initializing config prefix maps and gossiping them as appropriate from the range(s) that contain those config prefix keys (e.g. \0acct, \0perm, \0zone).

Test Plan:
Need to write unittests, but wanted to send this review before
getting on plane.

Reviewers: andybons

Differential Revision: http://phabricator.andybons.com/D45