Summary:
It makes more sense to just make this a settings panel rather than a standalone
app, particularly since setting panels are relatively well separated now.
Also default-disabled the SSH Keys interface since it won't currently be useful
for most installs.
Test Plan: Edited preferences.
Reviewed By: jungejason
Reviewers: tuomaspelkonen, jungejason, aran
CC: aran, jungejason
Differential Revision: 716
