[editor] TextEditor: Add more font sizes and fix default font size

Since no default size is set, the default font size is set to 16px, 
which is the browser(?) default on my PC.

projects/editor/src/app/text-editor/rich-text-editor.component.html

@@ -34,13 +34,20 @@
   <div>
     <mat-form-field>
       <mat-label>Schriftgröße</mat-label>
-      <mat-select [value]="editor.getAttributes('textStyle').fontSize?.toString() || ''"
+      <mat-select [value]="editor.getAttributes('textStyle').fontSize?.toString() || '16'"
                   (valueChange)="applyFontSize($event)">
         <mat-option value="8">8px</mat-option>
+        <mat-option value="10">10px</mat-option>
+        <mat-option value="12">12px</mat-option>
         <mat-option value="14">14px</mat-option>
         <mat-option value="16">16px</mat-option>
         <mat-option value="18">18px</mat-option>
+        <mat-option value="20">20px</mat-option>
+        <mat-option value="22">22px</mat-option>
         <mat-option value="24">24px</mat-option>
+        <mat-option value="26">26px</mat-option>
+        <mat-option value="28">28px</mat-option>
+        <mat-option value="30">30px</mat-option>
         <mat-option value="36">36px</mat-option>
       </mat-select>
     </mat-form-field>