PKCS#1 v2.2: RSA OAEP for forge.

This is a bit rough; I just copied-and-pasted this from my own project, and attempted to fit it into Forge where appropriate. Comments welcomed! Even better would be a careful review. There may be bugs still here, but I have been using it in an application that interoperates with output from Java, so it seems to "work". I hope!

Its very likely the test code could be refactored to use more internal Forge code (e.g., I really don't need to be using my own Base64 variant here

Fixes issue #20