Add catalogPath to datasets table in MySQL

[Marigold]

Right now we have to construct it ourselves as grapher/{namespace}/{version}/{shortName}. It'd be nice to have it there as a column, similarly to datasets.variables.

Implementation

• Fill catalogPath when upserting datasets to MySQL. Use the path to check if a dataset should be updated or inserted.
• Add an extra column tables with a list of tables in dataset (as JSON)