This conditional determines, whether the scanned assignment
specified by the `assignment` key is going to be hidden in the
digital version of the document. It is by default, but some style
files (`/mu/sci`) switch this, so that the scanned assignment is
included in the digital version.

Also removed a largely useless section from the guide.

class options, a list of `\thesissetup` keys relevant to the respective
faculty and detailed installation instructions. A section about the
recently added `\thesis@backend` macro was added to the Advanced usage
section.