Fixed: Open new tab in container if required

[ozars]

New tabs are opened in the panel's container if they're configured to do so.

Fixes #305.
Fixes #316.

Thanks for this great addon.

[ozars]

This will override containers of tabs opened from another pages even if the container of the parent tab isn't same as with the one set for the panel if "Open new tab in container" setting is enabled. I guess this behavior can be modified to respect parent's container if this is more convenient.

[ozars]

Uh-oh never mind. This looked like it worked, but it just shows as if it works in the GUI while not really setting tab's container properly. I figured after trying a container with SOCKS proxy and realized it doesn't actually update underlying container.

Not sure if this can be done without tabs.update() providing a property to update cookieStoreId for existing tabs or by reopening tab with correct cookieStoreId which is quite ugly. So, closing this PR.