Rework TrajectoryReporter

[CompRhys]

That is currently the default behavior but it's a bit convoluted. If no reporter is given:

static will make one when _configure_reporter is called.
When calling report the file IO will be bypassed in favor of a concatenation as you describe.
TrajectoryReporter probably needs a rework. Both to make it compatible with h5md (#19) and to make it easier to report out model properties, as you've identified.

For the latter, the simplest solution (perhaps not the best) would be to add the model_outputs as a optional kwarg to the report function so that model predictions can be covered by the current API without needing an additional call.

Originally posted by @orionarcher in #464 (comment)