Added new control MetroUserControl and flyout controls for it

Added the following controls:
Controls/MetroUserControl.cs
Controls/UserControlFlyout.cs
Controls/UserControlFlyoutsControl.cs

Added tab to demo to illustrate the new controls.

The purpose of these controls is to allow a user control to have its own flyouts.  In my project I needed to have flyouts for some user controls I created.  These additions allowed me to do so.  I am not in love with the control names but they get the point across.