Fix syntax highlighting for Docker and Yaml

[nuest]

prism.js already contains all languages, but the syntax highlighting for Dockerfile and yaml does not work, potentially because of the mime/type provided by the server.

The server gives Content-Type:text/yaml; charset=UTF-8 for erc.yml (client problem):

The server gives Content-Type:application/octet-stream for Dockerfile (probably server problem):

What is the type needed for Dockerfile?

[jansule]

Currently prism.js is only handling .Rmd files properly due to a change of the code highlighting framework. To make the highlighting properly running the o2rDisplayfiles.directive.js has to be edited. More precisely the functions here and here as well as here.