Added Key to GridViewColumnHeader for BasedOn

Added a Key to GridViewColumnHeader so it can be used in based on styles
Changed ComboBox Selection Style to better fit ListBox, ListView, etc. style

Changed ComboBox Selection Style to better fit ListBox, ListView, etc. style

-) Foreground AccentSelectedColorBrush when selected
-) Background AccentBrush when selected
-) Background AccentColor3 when mouseover
MetroTabControl uses MetroTabItems instead of regular ones when data binding.
Forgot to override the MetroAnimated*TabControls.
Fixes #411 by setting a font-size on the Clear button.

Signed-off-by: Amrykid <amrykid@gmail.com>
Merge pull request #455 from Amrykid/textbox-fontsize-clearbutton-bug

Fixes #411
Merge pull request #449 from stefan-schweiger/patch-2

Added Key to GridViewColumnHeader for BasedOn
Merge pull request #451 from Amrykid/tabcontrol-item-override

MetroTabControl uses MetroTabItems
Fixed the vertical alignment of the WindowsCommands

If the maximize, minimize and close buttons were hidden, the vertical
alignment of the WindowCommands was not centered
Overhaul for buttons, selection and texts
Fixed build, cleaned up XAML
Added field for the ComboBox control
Added sliders and progress things
Added tabcontrols to the demo
Added RangeSlider
Transitions
Added theme and accent changing options through in the menu

Oh and apparently the TextBlock "control" doesn't respond to theme
changing, so I had to replace every single one with a Label
Pre-select the selection controls
Added the Tile control
Merge pull request #463 from flagbug/windowcommands-fix

Fixed the vertical alignment of the WindowsCommands