Enhance workflow matrix for small screens

makes scrolling horizontally in the workflow manager easier.
The offline banner and the voting banner will lead to unwanted results.

client/src/app/site/motions/modules/motion-workflow/components/workflow-detail/workflow-detail.component.scss

@@ -40,5 +40,9 @@ table {
 }
 
 .scrollable-matrix {
-    overflow: auto;
+    overflow-y: scroll;
+    overflow-x: auto;
+    // the most simple solution that requires every other size to be exact.
+    // TODO: if the whole page is absolute again, this will not be required anymore.
+    height: calc(100vh - 128px);
 }