renaming Firefox-Accounts repos

[Brian Warner]

I just learned about a fifth repo, named "gherkin", which is a
replacement for the soon-to-be-obsolete "picl-gherkin". So the actual
list of renamings is as follows:

 * firefox-account-bridge => fxa-content-server
 * scrypt-helper          => fxa-scrypt-helper
 * picl-idp               => fxa-auth-server
 * picl-gherkin           => fxa-js-client-old
 * gherkin                => fxa-js-client

Renaming is now complete. Feel free to update your fork names and local
checkout remote URLs.

cheers,
 -Brian