v0.7.1

Changes:

• Improve AppBarToggleButton background color when checked
• Add compact sizing support for DataGridCheckBoxColumn
• Add ability to use the assembly icon
• Improve keyboard support for Flyout and SplitButton
• Fix visual glitch when opening a CommandBarFlyout with only secondary commands
• Allow arbitrary content in TitleBarButton
• Add TitleBar.Style attached property
• Fix issue where NumberBox compact mode popup doesn't disappear and is above all windows (#13)
• Refine window style