Prevent itemlist in classic cit and edit bibl dialogs from expanding

Also
- Cleanup the XUL of said dialogs
- Refactor, spearate and clarify custom CSS injection into FX XUL
  elements

scss/components/_selectItemsDialog.scss

@@ -36,4 +36,13 @@
         flex: 1 1 auto;
         margin-bottom: 8px;
     }
+}
+
+// richlistbox elements are crazy and will expand beyond the window size
+// unless all/most elements in the hierarchy that contain that
+// richlistbox have a min-height: 0 set
+.contain-richlistbox {
+    vbox, hbox {
+        min-height: 0;
+    }
 }