Improve comment-list view + 2 bug fixes

Comment-list view

- Display search bar only if comments exist

- If there are no comments yet, show only a big add-button

- Change sorting for participants to by time

General

- Show time in header only on desktop devices

- Fix carets/placeholder in several input fields

Closes #288 (closed)

src/app/components/shared/comment-list/comment-list.component.html

-<div fxLayout="row" id="search-container">
+<div fxLayout="row" id="search-container" *ngIf="comments.length > 0">
   <mat-label fxLayoutAlign="center center">
     <mat-icon class="search-icon">search</mat-icon>
   </mat-label>
@@ -72,6 +72,13 @@
   </mat-menu>
 </div>
 
+<div fxLayout="row" fxLayoutAlign="center" *ngIf="comments.length < 1">
+  <button mat-fab class="fab-extended" (click)="openCreateDialog()">
+    {{'comment-list.add-comment' | translate}}
+    <mat-icon class="add">add</mat-icon>
+  </button>
+</div>
+
 <div *ngIf="!isLoading">
 <app-comment *ngFor="let current of hideCommentsList ? filteredComments : comments" [comment]="current" [parseVote]="getVote(current)"></app-comment>
 </div>