Use DockPanel for Flyout

Using `DockPanel`, instead of `StackPanel`, for `Flyout`s.  This allows
content to scale on resize, it allows for forcing content to the bottom
of the `Flyout` -- such as confirm/cancel buttons.
Update MahApps.Metro/Themes/Panorama.xaml

The HeaderFontColor binding was not always working. And the problem and solution are described at http://stackoverflow.com/questions/4665645/cannot-override-labels-style-in-wpf
Update MahApps.Metro/Controls/Panorama.cs

Clicking a selected item should deselect it (i.e. toggle). This is particularly useful when the Panorama control is used to select multiple items.
Fixed GroupBox foreground color issue.
The panorama demo can be exited by pressing the escape key.
Added keys to ListBox and ListBoxItem for based on
Merge pull request #343 from stefan-schweiger/patch-1

Added keys to ListBox and ListBoxItem
Merge pull request #340 from Amrykid/panorama-demo-exit

The panorama demo can be exited by pressing the escape key.
Make sure timer is stopped on unload so panorama can be garbage collected
Merge pull request #335 from EvilClosetMonkey/master

Use DockPanel in Flyouts instead of StackPanel.
Merge pull request #344 from mrosack/master

Allow Panorama to be Garbage Collected
"save window settings elsewhere" scenario
Merge pull request #346 from punker76/customwindowsettings

"save window settings elsewhere" scenario
Merge branch 'master' of https://github.com/MahApps/MahApps.Metro

Conflicts:
	MetroDemo/IconsWindow.xaml