Added `\ifthesis@blocks@assignment@hideIfDigital@` to `mu/base` style.

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.

test/mu/compare/sci-digital-emptyassignment.tex

+\documentclass[digital]{fithesis3}
+\thesissetup{
+  faculty = sci,
+  assignment = {}}
+\begin{document}
+\end{document}

test/mu/compare/sci-digital-noassignment.tex

+\documentclass[digital]{fithesis3}
+\thesissetup{faculty = sci}
+\begin{document}
+\end{document}

test/mu/compare/sci-digital-someassignment-oneside.tex

+\documentclass[digital,oneside]{fithesis3}
+\thesissetup{%
+  faculty = sci,
+  assignment = {resources/blindtext, resources/blindtext}}
+\begin{document}
+\end{document}

test/mu/compare/sci-digital-someassignment-twoside.tex

+\documentclass[digital,twoside]{fithesis3}
+\thesissetup{%
+  faculty = sci,
+  assignment = {resources/blindtext, resources/blindtext}}
+\begin{document}
+\end{document}

test/mu/compare/sci-printed-emptyassignment.tex

+\documentclass[printed]{fithesis3}
+\thesissetup{
+  faculty = sci,
+  assignment = {}}
+\begin{document}
+\end{document}

test/mu/compare/sci-printed-noassignment.tex

+\documentclass[printed]{fithesis3}
+\thesissetup{faculty = sci}
+\begin{document}
+\end{document}

test/mu/compare/sci-printed-someassignment-oneside.tex

+\documentclass[printed,oneside]{fithesis3}
+\thesissetup{%
+  faculty = sci,
+  assignment = {resources/blindtext, resources/blindtext}}
+\begin{document}
+\end{document}

test/mu/compare/sci-printed-someassignment-twoside.tex

+\documentclass[printed,twoside]{fithesis3}
+\thesissetup{%
+  faculty = sci,
+  assignment = {resources/blindtext, resources/blindtext}}
+\begin{document}
+\end{document}