Add option to default to storing tabs to a single list only, not create a new list each time

[sken130]

Add option to default to storing tabs to a single list only, not create a new list each time. For example, if I store select page now, and store select page again, I would want the 2 pages in a single list, not 2 lists with 1 page each.

Implementation:

1. Perhaps, out of many lists, we could designate one list to be the default list
2. Add an option "Store new pages to default list instead of new list". If ticked, new pages should be stored to the default list rather than a new list each time.
3. Make sure shortcut of "store selected tab" should also respect the option in 2
4. (Only when the option in 2 is enabled) Add another option "Store page at the top of the list instead of bottom"

Motivation:

Often, each tab in my browser represents one task I have to do, and my job is really busy, and usually new tasks keep popping up before I am even able to finish the current task. So I need a way to put the current task (tab) to a shelf and handle it later. This is why I found this great extension to begin with.

Only one downside is, each time I store a tab, this extension creates a new list for me. This may be suitable for other use cases, but for task management, I would prefer my tasks in one single list instead of separate lists.