Build utils library without ROOT

The commits in this PR remove the ROOT dependence of the utils library (/utils/*) and also remove the dictionary generation for this library. Please comment if the dictionary for the utils library fulfils any important function within the GUI that I've not been aware of -- the dictionary could then still be built if the GUI is also being compiled.

The utils library can now be built separately by using ```cmake -DBUILD_utils=ON ..```. It will automatically be built if the GUI is also built.

This allows to use the utils e.g. in CLI utilities without needing ROOT and addresses issue psi46/pxar#94.
Furthermore, it removes problems with the dictionary generation on various platforms seen in issues psi46/pxar#20, psi46/pxar#98, and psi46/pxar#105.