Fixes issue #4
Issue #4 also fixed for AppBarToggleButton
Added additional check for type in AppBarToggleItemCommand.OnAttached (see issue #4)
Merge pull request #5 from frostieDE/master

Fix two issues, one for the IsEnabled for a checked command, the other for the IsCheck state. Go to https://github.com/allenlooplee/AppBarUtils/issues/4 for more information.