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
Since we're using `\/` as a better `Either` (and I agree we should), it might be best to use `\/.fromTryCatch` as well instead of Scala's `Try`.  That would mean your return type would become `Throwable \/ String`.