Hall A Analyzer

Handling of prescale events was lost with the move to the object-oriented decoder. We need to write an event type handler for the prescale events. Some initial inspection shows that just adding a handler won't be enough. The prescale factors are needed at run initialization time, for which a separate instance of the decoder is instantiated. Since event type handlers are not part of the decoder anymore, we will now also need to instantiate all event type handlers. But do we really? Event type handlers may include a full analysis chain, but we only need the "RawDecode" part of it. This points to deeper design flaws with the event type handlers. The design needs to be reviewed and additional functionality probably needs to be added.

Aside from the missing prescale decode feature, there is also a bug: Run initialization succeeds if a prescale event is present, regardless of whether prescales have actually been decoded. Successful decoding also needs to be checked.