Phantomjs not platform independent

[markusbaumeister]

The current version of phantomjs (in doc/) is the one for Linux (64bit). The support for animations should be extended to Mac and, ideally, Windows.

Since manual building is very resource consuming (compare https://phantomjs.org/build.html), it would probably be better to have all compiled phantomjs-versions (https://phantomjs.org/download.html) and to recognize the correct version upon first executing the Makefile.