use Papis opentool

[jghauser]

No description provided.

[jghauser]

I just realised that this needs some more thinking because (a) Papis will always have its own opentool settings, so we don't need them in papis.nvim and (b) we can't just run the opentool as a command as the Papis option might include arguments (so we need to split the string to get the command + args). I also noticed there's a difference between the default windows opener, and I'm not sure if that matters.

[jghauser]

Just a small explanation: papis.nvim now always uses the opentool defined by Papis. This should work as Papis will by default set that to something that works for the OS on which it is running.