Produce live output

[gcrois]

Currently, execution of commands only produces output upon their completion.

Commands that take a long time (i.e., apt/pip install) present no indication that execution is continuing, potentially leading the user to believing that their session has halted.

Furthermore, commands which require user interaction (apt install) have no way of continuing execution.

It appears that an earlier version of process listening (like in https://github.com/UTK-PAIRS/avocat/blob/0e6552999318571c3290e8e39e95d22795fa5e39/avocat/main.py) may be necessary.