Use proper syntax highlighting on the server

We have many places on the server where we could benefit from proper syntax highlighting - these include job parameters, groovy code, file content in the sandboxes view, graph logs, ...
Currently, many of these places even use proportional font (see CLO-2301) making the usage quite painful when code or file content is involved. Please implement proper syntax highlight for code and file content in the Server GUI. There are many libraries which can be used for that, but CodeMirror seems to be recommended very often. It is pure javascript (i.e. client side only - no need to bother the server with the complex stuff) and is released with MIT license thus it can be used commercially. It is actually used for example by Google and many others.