Python: Should we provide further completions after a completed a magic/shell command?

[seeM]

Currently if you type e.g. %cat <cursor> or %pinfo <cursor> you will not receive any further completions. It would probably be useful to receive path completions in the first case, and object completions in the second. Maybe a good heuristic is to provide all Jedi completions after an explicit magic command followed by whitespace?

We also don't currently receive completions after an explicit shell command like !cat. Maybe we could provide only path completions in that case? There's a further complication that IPython allows the syntax !cat {filename} and replaces {filename} with str(filename) where filename can be any local variable.