Replace custom string loading

As part of the first step in the plan to convert the Channel Manager to Angular we plan to replace custom string loading.

We read SVG, font, hippo-iframe.css as string. Instead of injecting strings we could inject links? (to css file, to svg files). To research: can Angular CLI generate multiple .css files? (one for the app, and one for in the iframe).

The complete plan can be found here: https://docs.google.com/document/d/1RoGCnJSBXrvP0kdd0jGLzWNd6Cbv1ucCpbo0YLNUN5c