initial version of the query autocompletion

Missing features at this point:
1. No suggestions when the input gets the focus.
2. Suggestions are not shown after selecting a suggestion.

pdb-js/src/app/query-autocomplete/query-autocomplete.component.html

@@ -0,0 +1,16 @@
+<input matInput 
+  type="text"
+  id="query-autocomplete-input"
+  placeholder="Query" 
+  [formControl]="query"
+  [matAutocomplete]="auto" 
+  (keyup)="onKey($event)"/>
+<mat-autocomplete 
+  #auto="matAutocomplete" 
+  [displayWith]="displaySuggestion"
+  >
+    <mat-option *ngFor="let suggestion of filteredSuggestions | async" 
+      [value]="suggestion">
+      {{suggestion.value}}
+    </mat-option>
+  </mat-autocomplete>