Added the ability to select multiple items on the listview

[GrantByrne]

This change allows the user to select multiple items on the list view. This can be used to:

• Bring to focus multiple windows
• Close multiple windows at the same time

This closes #63

[kvakulo]

Hi @holymoo!

Thank you for your PR 🥇

I'm sorry to only accept it now after such a long time. Better late than never I guess :smile:

/ Regin