Add support for saving/restoring tab groups

[0xdevalias]

It would be cool if Sesh was able to save/restore tab groups within a window. The way I envision this working at the bookmark level is that it would probably create a sub-folder per tab group, with the sub-folder name being the tab group name.

This is something I've had in the back of my mind for ages, but haven't made time to work on it yet to be able to submit a PR/similar.. though ideally I might get to it at some stage still.

Semi-related research:

• Support for Chrome's Tab Groups 0xdevalias/chrome-NewWindowWithTabsToRight#10
• Save/Restore tabs 0xdevalias/chrome-NewWindowWithTabsToRight#6