New BeamDataPoint definition prevents access to BeamStatus objects in old processed files

[mnieslony]

Hi @atcsutton,

I just noticed when pulling the changes from PR #241 that I am afterwards no longer able to access the BeamStatus object in processed ANNIEEvent files that have been processed before this PR.

I suppose this is the case since the BeamDataPoint object now has an additional time member variable and the BeamStatus object stores information in the form of BeamDataPoints (among others). Now the BeamDataPoint objects in the old processed files do not match the new object definition, causing a crash when trying to access the objects.

Could you maybe have a look at this and verify? Maybe I'm just doing something wrong... When reverting to the old BeamDataPoint definition, I can access the BeamStatus objects fine.

Not sure if there's an easy fix, but it would be good if one could still access the BeamStatus information in previously processed files, so maybe we also could have a new version of the BeamDataPoint object for the BeamFetcherV2?

Thanks!