Added light & dark theme. Basic theme applied on dialogs/modals. Attempt to apply uniformity to the website.

src/app/groups/group-item-edit/group-item-edit.component.html

@@ -38,13 +38,15 @@
       }
     </mat-form-field>
   </mat-card-content>
-  <mat-card-actions align="end">
+  <mat-card-actions>
     <button mat-button
+            class="neutral"
             [disabled]="waitForResponse"
             (click)="cancel()">
       <mat-icon>cancel</mat-icon>Cancel
     </button>
     <button mat-button
+            class="confirm"
             [disabled]="waitForResponse || formGroup.invalid"
             (click)="add()">
       <mat-icon>add</mat-icon>Add