Improve toolbars on small screens

- normalized toolbars in message viewer, contact viewer and contact
  editor;
- lower width of sidenav on medium screens;
- reworked display of message headers

UI/WebServerResources/scss/components/button/button.scss

@@ -108,7 +108,7 @@ md-list md-list-item button.md-button.sg-icon-button {
 .sg-icon-bar--vertical {
   display: flex;
   flex-direction: column;
-  margin: 0 ($mg * -1) 0 $mg;
+  //margin: 0 ($mg * -1) 0 $mg;
   font-size: $sg-font-size-3;
   align-items: center;
   // Containers have padding, we compensate to align according to specs