Enable searching for posts by id from Keyword search, refs T731

Test Plan:
Search for "99", "95", or "1" from Keyword.
Search for "test" from Keyword.

Reviewers: aMoniker, rjmackay

Reviewed By: rjmackay

Subscribers: bodacea, srutto

Maniphest Tasks: T731

Differential Revision: https://phabricator.ushahidi.com/D348