Allow saving whole session with all workspaces

[takinoy]

Work in progress

Made a pull request for this feature:

• i3-resurrect save/restore --session to save whole session
• i3-resurrect save/restore --workspace list-of-workspaces for saving multiples workspaces
• i3-resurrect restore --session --clear for deleting active workspaces before restoring.

This implementation use subdir for saving profiles instead of files, to allow saving multiples workspaces or whole session profile

this may be usefull for some people

[TheBlackArroVV]

Would this feature be finished in the future?

[takinoy]

Would this feature be finished in the future?

I made some changes on this feature in my repo, may need some further testing...

[Thaodan]

When would the program to be ran to save the session? Is there a hook to hook into to be called before the session ends. Same for restoring them.