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
Is there a consensus or preferred approach to creating explicit lefts and rights by the way?  I tend to use `foo.left` and `foo.right` instead of `-\/(foo)` or `\/-(foo)` but could be convinced otherwise.