fix os logic

public/views/partials/child.hbs

@@ -7,7 +7,7 @@
         {{#if this.printable}}
         <button data-tooltip="Drucken" id="printbutton">🖨</button>
         {{/if}}
-        <button class="close">✕</button>
+        <button class="close">X</button>
       </div>
     </div>
     <div class="window-content">

public/views/partials/window.hbs

@@ -8,9 +8,9 @@
         {{#if tutorial}}
         <button class="tutorial" id="tutorial-{{appname}}-{{label}}" onclick="tutorial.start()" data-tooltip="Startet eine interaktive Einführung">&#128161;</button>
         {{/if}}
-        <button class="minimize">🗕</button>
+        <button class="minimize">▽</button>
         <button class="maximize">{{#equaler state "==" "maximized"}}🗗{{else}}▢{{/equaler}}</button>
-        <button class="close">✕</button>
+        <button class="close">X</button>
       </div>
     </div>
     <div class="window-content">