Rewrite db sync script to parse Gatherer by expansion

["the Phoeron" Colin J.E. Lupton]

A naive loop over all possible Multiverse IDs, and a similar attempt at compiling a list of valid Multiverse IDs (per issue #4), is far too slow and error prone.

A better approach is to pull the list of Multiverse IDs, and total card count, from the Gatherer expansion set page with the visual spoiler output (since it is not paginated).

["the Phoeron" Colin J.E. Lupton]

One issue with this approach is that it does not factor in variations of the same card, or two-sided cards.