Fix for #1235

Reset all mouse drag related events when ShowTitleBar is changed.
Moved SetWindowsEvents to end of ToggleVisibiltyForAllTitleElements
fix SizeToContent for MetroWindow
add a little demo
Merge pull request #1262 from MahApps/1231-punker76-SizeToContent

fix SizeToContent for MetroWindow
Merge pull request #1255 from iankerr/master

Fix for #1235
SizeToContent should work after window loaded