Add change password settings panel

Summary:
In password-based auth environments, there is now a user settings
panel to allow them to change their password.

Test Plan:
Click settings, choose password from the left:

• enter current password, new password (twice), log out, and log in with new password
• enter current password, non-matching passwords, and get error
• enter invalid old password, and get error
• use firebug to change csrf token and verify that it does not save with and invalid token

Changed config to disable password auth, loaded settings panel and saw
that password was no longer visible. Tried loading the panel anyway and
got redirected.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: 890