make the drop down for "combine with" dynamic

pdb-js/src/app/visualization-page/visualization-page.component.html

@@ -7,19 +7,21 @@
       <input matInput placeholder="Query" value="{{query}}" />
   </div>
   <div id="filters">
-    <button mat-button>
+    <button mat-button (click)="plot()">
       <img src="assets/img/scatter-chart2.svg" class="icon-inline" aria-hidden="true" title="create plot" />
       Plot
     </button>
-    <button mat-button>
+    <!--
+    <button mat-button (click)="gallery()">
       <img src="assets/img/four-squares-line.svg" class="icon-inline" aria-hidden="true" title="Create Gallery (only active if 'Split' is set)" />
       Gallery
     </button>
+    -->
     
   
     <mat-form-field>
       <mat-label>Type:</mat-label>
-      <mat-select [(value)]="selectedPlotType">
+      <mat-select [formControl]="selectedPlotType">
         <mat-option *ngFor="let plotType of plotTypes" [value]="plotType.name">
           <img src="assets/img/{{plotType.icon}}.svg" class="icon-select" /> {{plotType.name}}
         </mat-option>