Introduce DropDownButton
Some small fixes
Fix opening contextmenu issue
Merge pull request #1158 from QuantumDeveloper/DropDownButton

[WIP] Introduce DropDownButton
add DefaultText Property
use the default text in the input dialog
MetroDialogSettings.DefaultText = ""
ensure find the resources

when it do not have the app.xaml...
Merge pull request #1160 from ye4241/master

make the input dialog support for default text