Restore "author" link to diffusion

Summary: create the page by getting data from the search result.
Test Plan:
load page with url /author/, /author/valid_username, and
/uathor/invalid_username, and verified that it works as expected.

Reviewed By: epriestley
Reviewers: epriestley, tuomaspelkonen
Commenters: tuomaspelkonen
CC: hwang, aran, tuomaspelkonen, epriestley, jungejason
Differential Revision: 723