Simplify the storage.js interface

* Remove setLoggedIn and getLoggedIn
* Remove signInEmail namespace

Data is now handled by the storage.site.set/get functions with approprite namespace keys. This is to make where this info is stored consistent with other site specific info.
builds on get_assertion to post to a verifier and check the response; useful for aws and other buildout
Add tabindex attributes to the TOS/PP links.

Allows users to tab directly from the email/password field to the submit button.

fixes #3079
set agent:false for requests
Merge pull request #3217 from jrgm/agent-false

set agent:false for requests
Merge pull request #3209 from jrgm/check_verifier_can_verify

builds on get_assertion to post to a verifier and check the response; useful for aws and other buildout
Merge pull request #3214 from mozilla/issue_3079_tabindex_tos

Add tabindex attributes to the TOS/PP links.
Merge pull request #3150 from mozilla/simplify_storage

Simplify the storage.js interface