(ReindexAll) Added principals reindex-all

Complete:
* SearchAPI methods to register handlers
* Generic "iterateAll" helper in cassandra.js
* Principals reindex-all handler
* Global admin REST endpoint to trigger

Todo:
* Unit tests
* Content reindex-all handler
(ReindexAll) Start tightening up for unit tests. Still no actual tests written.
(ReindexAll) Added unit tests for iterateAll functionality
(ReindexAll) Addressing issues with tombstones. Added unit tests for content and principal iterateAll