FEATURE REQUEST: Allow to open TODOs outside of the project

[schellenbergk]

Use Case:

I don't like to commit my todos with my source, and I keep them outside of my project in a cloud (eg. project1.todo, project2.todo, etc.). That way when i pull the project from Github on a new computer, I can just open related todo from the cloud.

Currently Todo Open command, auto creates TODO in the project root folder. Either Add Open External or allow to choose a custom filename/location when opening new todo.