Allow opening an item in a new window

Sometimes, it would be useful to have two items open at once. For example:

• I have one todo list where I maintain a "cooking" plan, with one todo per day to represent what to cook at that day.
• In another todo list, I add one todo per week to collect what to buy that week.

It would be nice to have both open side by side, so I can plan what to cook and - in parallel add items to the grocery list.