Add ETTC to output

@anilbey we don't have to do it for the current mm we're running.
But could you add an ETTC (estimate time to completion) message to the output of bluepymm.
Bluepythresh has such a feature (in run.py)

Start by reading the ETTC implementation in Bluepythresh's run.py, then trace how BluePyMM produces its output. Determine where the corresponding message belongs and compare the resulting output with the referenced feature. Done means bluepymm reports an ETTC message without requiring changes for the current model run.

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