add outbound HTTP proxy support to browserid - requires a proxy that can forward http to https traffic - closes #904

move 'primary.js' - abstraction for interacting with primaries - down to lib/, now it's used by different processes

implement support for verifying assertions issued by primaries for the purpose of logging into browserid

implement a more generic mechanism to enable local testing and development of primary support - allow SHIMMED_PRIMARIES to be provided which stuffs a auth url, provisioning url, and public key in our cache

implement a more generic mechanism to enable local testing and development of primary support - allow SHIMMED_PRIMARIES to be provided which stuffs a auth url, provisioning url, and public key in our cache