Added Oda.FileManager

This is a work in progress.  Used for testing Oda.Ajax.  Totally
insecure, should not be used at this point.
Seperated AuthenticationPlugin class from Session.cs

Each class should have its own file.  I'll keep trying till I get it
right.
Altered callback message for UpdateContact

Now with words!
Finished Oda.Ajax.

Huge undertaking, took 700% longer than I thought becuase I added file
upload.  Only works in HTML 5 right now.  Backwards compatibility will
come later.
Added file upload capability.

This was no simple task.  It should be transparent to the user of the
API.  Soon: Progress event handlers in HttpModule.