Allow renderjs from JS only, without initial gadget-tag/script-tag

Genereal

In order to integrate renderjs and jupyter I need to be able to load everything-renderjs from a javascript interface. The inital loaded HTML does not contain anything of renderjs and gets added only after pageload.
I thus added functionallity to renderjs to initialize manually, after pageload. See the forum entry here.
Instead of registering init() for the DOMContentLoaded event directly, a deferred promise is used which gets resolve either by the event, or by a manual call of rJS.manualBootstrap().

Injects rsvp/renderjs in a blank iframe
makes sure renderjs is only present after it was injected
calls manual bootstrap to initialzed renderjs
creates small test gadget to ensure renderjs is working within the iframe (after bootstrap was executed)