Option to fit box size

[blairlyons]

Use Case

As a user converting data from a supported source, I want to be able to set the box size to fit around the spatial data, rather than having to provide it.

Acceptance Criteria

On MetaData, include a fit_bounding_box bool option, which will override the box size using the extents of the data.

Details

If fit_bounding_box` is True:

• find the min and max extents of the positions in X, Y, and Z during conversion (use numpy.amin() and numpy.amax() with axis arguments after reading in all the positions)
• override meta_data.box_size with (max - min)
• if also centering trajectory, calculate the new box_size first