Adding support for embedded resources

Refactored BaseDir slightly to use the the same TemplateResolver class to resolve the actual file served. 

Add two keys to your configr:

		<add key="razor.email.embedded" value="true"/>
		<add key="razor.email.assemblyName" value="Your.Assembly"/>

And RazorMailer will attempt to pull the templates and config from the configured assembly as an embedded resource vs. file-base.

This change was specifically made locally to support RazorEmail in an Azure WebWorker role, which doesn't seem to support file-based templates.