TextEditor: Increase zoom limit to 3000%

Zooming using the mouse wheel has no upper bound.

Change-Id: I7ff680c7b48fb4d01773a3479bf17e3d81da7de7
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/texteditor/fontsettingspage.ui

@@ -78,7 +78,7 @@
          <number>10</number>
         </property>
         <property name="maximum">
-         <number>300</number>
+         <number>3000</number>
         </property>
         <property name="singleStep">
          <number>10</number>