OCSADV-27: Model and parser for VoTable

Model, Parser and tests for VoTable xml. The main public function takes an xml node and returns a list of resources containing sidereal targets. Likely, there will be changes to the model as it is integrated into the AGS and UI

As much as possible the parser tries to retain parsing errors, but at the same will extract as many valid targets as possible
I think you may be able to do this with `traverse` but i'm not 100% clear on the logic. I think it might be good to pull this nested `for` expression out into another method.