Add Reddit and Twitter Oauth providers

Added Reddit and Twitter support.

Twitter requires request signing for every transaction.  There are no native JavaScript functions for HMAC-SHA1, required for signing.  To use the Twitter provider, the open source library, jsSHA, must be included in the HTML file.

The Twitter login process can be seen here:

https://dev.twitter.com/web/sign-in/implementing

Failure to include jsSHA will not negatively impact the other service providers.