Enable typeahead's ondemand on details view page

Summary:
the details pages are using preload instead of ondemand for
typeahead, but the most common actions on the pages are commenting which
would not need the preloaded info. To improve the performance of the
pages, turn on ondemand according to the setting in the config file.

Test Plan: verify it is working with both modes, for both pages.

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 995