Support restoring project eshell and dired buffers in tabspaces

[ParetoOptimalDev]

Feature request adding to #18.

I find that sometimes I'll only have a project-eshell buffer or dired buffer open from doing C-x p c or C x p p RET.

This means when I restore a tabspace there's not really a project open anymore ebcause those buffers aren't restored.

I then have the mild inconvenience of having to do C x p p to select the project again and reopen the dired or eshell buffer.

This request doesn't include restoring eshell output or anything, just essentially adding "this project had only an eshell buffer open so we'll do C-x p c on tab restore in that directory" logic.

[mclearc]

This is certainly a fair request. I initially supported only file-visiting buffers because that was the simplest thing to do. But shell buffers, maybe dired buffers, etc. would be nice. So I'll look into supporting this as well, though I may not be able to get to it immediately.