Settings and delete account screens.

Start on the manage page and delete account screen.

* Update the settings screen
* Add one new screen, /delete_account
* Add new auth-server functions to the fxa-client to handle changing a password, signing out, and deleting an account.
* Update session state directly from fxa-client.js instead of in views to reduce boilerplate code.
* Remove a lot of View display boilerplate by creating a generic function showView
* Save Session data to localStorage to keep a client side cache of info and fix #310

issue #254