Add style and help button.

frontend/src/app/pages/publication-edition/publication-edition.component.html

@@ -47,6 +47,9 @@
                             <button type="button" disabled matTooltip="Click to insert a code block">
                                 <mat-icon>code</mat-icon>
                             </button>
+                            <button type="button" disabled matTooltip="Click to display editor help">
+                                <mat-icon>help</mat-icon>
+                            </button>
                         </div>
                         <mat-form-field class="example-form-field">
                             <mat-label>Content</mat-label>

frontend/src/app/pages/publication-edition/publication-edition.component.scss

@@ -130,6 +130,11 @@ button, a.button {
         cursor: pointer;
     }
 
+    &:disabled {
+        background-color: #5f6aa6;
+        cursor: not-allowed;
+    }
+
     &.secondary {
         color: #3f51b5;
         background-color: white;