Update schema station data to include full chain of custody

[bkeepers]

As #52 makes very apparent, the data is often derived from a long chain of custody.

For example, the brest-822a-fra-uhslc_rq station:

• Systeme d'Observation du Niveau des Eaux Littorales (SONEL)
• Centre Littoral de Geophysique (CLDG)
• Universite de La Rochelle France in collaboration with Service Hydrographique et Oceanographique de la Marine (SHOM) France 
• University of Hawaii Sea Level Center (UHSLC)
• GESLA
• TICON

It probalby make sense to change the source field into an array.