initial sketch of preVerifiedTokens
added a test for invalid preverifytoken, default config to no secret
WIP on public-key preVerifyTokens
use b64url encoding for JWKs as in the spec
config cleanup
stub docs fro preVerifyToken
test re-create with preVerifyToken
more input validation of preVerifyToken with regex
more preVerifyToken docs, strictSSL
removed iss from preVerifyToken JWT
cosmetic changes to preverifier functions
ensure the preVerifyToken sub is defined
api.md formatting
added 'use' to JWK
JWK 'use' should be 'sig' not 'sign'
Merge pull request #784 from dannycoates/pvt

Support for preVerifiedTokens in /account/create to allow trusted reliers who have already verified the the user's email to more easily transition users to FxA. A valid preVerified token allows the user to skip the email verification step, i.e., the user's account is verified after /account/create completes.

fixes #780
r=rfk,ckarlof