real-time analysis output

[ijpulidos]

To have a way to know how is our simulation performing in "real time", perses can generate a computer- and human-readable file (YAML?) with at least the following information:

• progress: current iteration, max iterations, percent progress
• free energy estimates: DDG, dDDG, number of uncorrelated samples
• performance: ns/day, wall clock time per iteration, ETA for completion

We could use/revive what's in the MultiStateSampler in openmmtools.