Add linter to arcanist config.  Fix whitespace errors

Summary:
Arcanist text linter to detect basic formatting problems like
tabs and trailing whitespace.

Clean up whitespace errors to avoid noise in future diffs
from whitespace fixes

Test Plan: Still compiles ok

Reviewers: emayanke, dhruba

Reviewed By: emayanke

Differential Revision: https://reviews.facebook.net/D8301