Update framework/source/class/qx/ui/form/VirtualComboBox.js

Correction to do a better support for empty selection
Minor typo fix.
[BUG #6860] First draft of a new tutorial app.
[BUG #6860] Editor is working now. Additionally styled the app to look like a qooxdoo demo app.
[BUG #6860] Updated description to show the first (test) tutorial.
[BUG #6860] Use bom.request instead of old script loader.
[BUG #6860] Make sure the former app gets removed.
[BUG #6860] Minor styling.
[BUG #6860] Load the tutorials as HTML file and not as Class.
[BUG #6860] Moved back the code to a qooxdoo class to make sure its considered during dependency analysis.
[BUG #6860] Added content of the hello world tutorial.
[BUG #6860] Highlight code in the tutorial.
[BUG #6860] Minor.
[BUG #6860] Added window for the selection of tutorials.
[BUG #6860] Add a select button and update the view on selection change.
[BUG #6860] Update the next button on setting a new tutorial.
[BUG #6860] Added mode switch for mobile tutorials.
[BUG #6860] Improved config for including android css.
[BUG #6860] Added mobile sample dummy.
[BUG #6860] Use split panes for the main layout.