Keyboard support
    A critical requirement for software accessibility is keyboard support as a complete
    alternative to pointing devices (mouse, etc.).
    Keyboard support is comprised of command key, focus key, and keyboard navigation.
    RadTreeView will seamlessly switch between mouse and keyboard navigation.
    In order to configure keyboard support with RadTreeView its KeyboardNaviagationSettings should be set:
<telerik:RadTreeView ID="RadTreeView1" runat="server" >
    <KeyboardNavigationSettings CommandKey="Alt" FocusKey="M" />
</telerik:RadTreeView>
    The KeyboardNavigationSettings exposes two properties to configure
    the keyboard combination that sets focus to the control:
    - FocusKey: An upper-case letter or number.
- CommandKey Ctrl , Alt, Shift, or any combination of two of these keys.
    When there are multiple TreeViews on a given page, each of them may have a different activation combination.
    In this particular example, the [CommandKey] and the [FocusKey] can be customized in the Demo Configurator.
    Once the RadTreeView is focused (by pressing [CommandKey] + [FocusKey]) the user can:
    - Navigate through the nodes using the Down Arrow and  Up Arrow.
- Expand/collapse a node using the +  /  -  Numpad keys 
        or Left Arrow / Right Arrow .
- Select a node using the Enter  key.
- Check / Uncheck a node using the Space  key.
    Note: It is recommended to avoid [CommandKey] + [FocusKey] combinations matching keyboard shortcuts used in browsers.
    If the combination coincides with an existing browser shortcut the control may be unable to focus.