Add option to "Track closed windows"

[pmolodo]

Is your feature request related to a problem? Please describe.
When using a tracking session, with "Track newly opened windows" on, I find it frustrating that when I re-open a previous session, I then have to go and re-close a bunch of windows that I had already closed, and then go and remove them from the session in the TSM interface as well.

Describe the solution you'd like
Ideally, I'd like a solution that would allow me to seamlessly continue a browser session, remembering which tabs and windows were open. A tracking session with "Track newly opened windows" on is almost there, except that it doesn't remember which windows I have closed - something which happens frequently in my workflow.

An option, similar to "Track newly opened windows", to "Track closed windows", which would simply remove windows from the tracking session if they are closed, would get me to the seamless save / continue workflow I'm looking for.

There would need to be a few exceptions:

• you wouldn't remove windows from the session if we're quitting the browser
• you wouldn't remove a window if it's the last one in the session

Describe alternatives you've considered
PR187 seems to implement the feature I would desire (as well as some other fixes), including the desired exceptions:

• Quitting the browser does not remove windows from tracked sessions
• Closing all windows does not remove the windows from the tracked session