Add code-block dialog and style it.

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

@@ -44,7 +44,7 @@
                             <button type="button" matTooltip="Click to insert a link" (click)="insertLink()">
                                 <mat-icon>link</mat-icon>
                             </button>
-                            <button type="button" disabled matTooltip="Click to insert a code block">
+                            <button type="button" matTooltip="Click to insert a code block" (click)="displayCodeBlockDialog()">
                                 <mat-icon>code</mat-icon>
                             </button>
                             <button type="button" disabled matTooltip="Click to display editor help">