Support for Token Replacement

[mitchelsellers]

The current implementation of the Email Template Factory allows for a final email message to be integrated into a template.

This should be expanded to allow users to provide a second template, which would be pulled from the same location, but used for the actual content. For example.

BuildTemplatedMessage(string templatePath, List<KeyValuePair<string, string>> tokens);

This could then be chained with the BuildEmailContent() call.