Shimming toolbox soft dependencies during the installation

[po09i]

The script used to install the plugin allows to easily install everything that is a hard dependency, however, soft dependencies such as SCT, prelude and dcm2niix are not considered (dcm2niix comes with fsleyes so we are fine) (prelude comes with FSL so maybe it is also covered but we would have to check)

This means the script does not "fully" install shimming toolbox, we should mention that somewhere to the user/find a way to handle this.