Workflow integration events/callbacks

[acdha]

We've currently been working on this as a standalone application but it would be useful to have a way for someone integrating this into a larger process to be able to direct the user to the next stage – that seems like an argument for either emitting JavaScript events at key points (e.g. bag finalization / upload complete) so they could e.g. redirect to the next page after the user indicates that the bag is complete.

[acdha]

@eikeon Mostly leaving this here as a place to collect our discussion notes but perhaps e.g. @edsu, @dbrunton, @kzwa will be able to contribute some integration examples beyond the ones we've talked about.