Remove redundant WindowButtonCommands WPF controls

One less Grid control and one less Path control in the
WindowButtonCommands' default template, the same behavior holds.
Optimizing for less WPF controls is always good.
Note: Also fixed some typos.
Use a DataTrigger instead of the Converter
Changed FrameworkElement to DependencyObject
Merge pull request #1508 from Dotnetifier/FlyoutCloseFix

Flyout close fix
Merge pull request #1504 from mrahhal/optimize-use-of-wpf-controls

Remove redundant WindowButtonCommands WPF controls