Treeview Examples: Remove keypress events and use images instead of entities for visual state information

* removed keypress events
* use images instead of entities for visual indicators of expanded/collapsed states.
* Removed white space formatting errors in:
    1. examples/treeview/treeview-1/js/treeitem.js
    2. examples/treeview/treeview-2/js/treeitemLinks.js

Author: jongund