Create javascript pipeline

[schneijan]

In order to improve the loading times of the frontend, we urgently need a javascript pipeline that prepares the javascript before creating the WAR. It should include:

• Concatenate all javascript files into one single file
• Minify this file

It would be great if we could switch between a development (without pipeline) and a productive version (with pipeline).

We could use wro4j for this purpose which is already part of the MBP, but there are also promising alternatives.