R1:d0b6602e294d

Add an option to switch tokenizers to use "ondemand" instead of "preloaded"
datasources

Summary:
The open source Phabricator has like 3,500 user accounts now and it takes a
while to pull/render them. Add an option to switch to ondemand for large
installs.

I'll follow up with a patch at some point to address a couple of name things:

- Denormalize last names into a keyed column (although this evidences some
bias toward the western world).
- Force all usernames to lowercase (sorry Girish, Makinde).