Add API call or calls to query online spectral line catalogue(s)

[DJWalker42]

Users should be able to select particular spectral lines for their observations based on the spectral windows they define. Those lines (and accompanying meta-data) should come from an online catalogue(s) e.g. Splatalogue.

[DJWalker42]

If this can be done in the frontend, then it should be done in the frontend, c.f. SIMBAD integration for the GUI.