Fixed DataGridCell selection behavior

Before you had to click exactly an the TextBlock to select the row, now
you can click on the whole row.

Thanks @stefan-schweiger
Allow more items to be displayed in the ComboBox autocompletion demo
Removed unecessary property
Fixed a bug where closing a tab would result in a NullReferenceException. Added a property when a MetroTabItem is created by a Metro*TabControl.
Merge pull request #517 from Amrykid/metro-tabitem-patch1

MetroTabItem Patch #1
CloseTabCommand should work /better/. All TabControls inherit from BaseMetroTabControl in order to make extending the TabControls easier.
Reworked TabItem Close button infrastructure. Close Button isn't show until the tab is selected or has mouse hover. CloseTabCommand is only called on MVVM Data Bound items.
Added a TabItemClosingEvent where the user can cancel the closing of a TabItem for non-databound TabItems.
A MetroTabItem is only auto-generated from data bound items.
Fixed the TabItem datacontext issue for now. Temporarily worked around the TabControl Unload issue.
Fixes #387
Added TabStripPlacement to the Metro*TabControls that did not have it. Fixes #527
Oops, forgot to remove the TabStripPlacement from MainWindow.xaml.
Fix TabStripPlacement bug (#527) in default tab control style and make a sample
Merge pull request #528 from snowdreamist/master

Fix TabStripPlacement  bug(#527) on system default TabControl
Merge pull request #520 from Amrykid/metro-tabitem-patch2

[RFC] Metro TabItem/TabControl Patch #2
Merge pull request #523 from Amrykid/flyouts-bindable

Fixes #387
Fixes #529 - uses @cwford's P/Invoke code
Fixed a bug with titlebar-less windows losing their ability to be dragged. It came from my fix of 10343ae838b9888e409bdf3371b914ee4d33bb45
Removed the commented code.