Initial hack on an underlined TabControl
Add the basic flags
Add the basic properties and create the overlay behavior for Flyouts
Remove ShowWindowButtonCommandsOnHiddenTitleBar and replace it with the new overlay behavior
Use the HasFlag method
Create the titlebar overlay behavior for all elements
Don't overlay the icon by default
Move test helpers around
Fix up the Flyout tests
Move that to Controls
Don't propagate the mousdown event when any flyout is closed

Fixes #1411
Merge pull request #1428 from MahApps/fix-1411

Don't propagate the MouseDown event when any Flyout is closed
Merge pull request #1430 from GeertvanHorrik/master

Support runtime accents
Added templating for the mouse over when the `DataGrid` has `SelectionUnit=Cell`.
Fixes #975
Modified trigger for the cell color when selected

Corrected the issue that the active selection was not the correct color.
Unfortunately, the active selection mechanism doesn't work when the datagrid is in "selection unit cell". Therefore, I used the AccentColor for the Cell selection.
Added DataGrid example for selection unit cell
Merge pull request #1446 from Gimly/master

Fixed templating issues when the DataGrid has SelectionUnit=Cell
simplify datagrid example
set background for DataGridRow
Merge pull request #1448 from MahApps/punker76-simplify-datagrid-example

simplify datagrid example