Provide option to use cached dimensions and/or query IDs

[DylanBaker]

It is sometimes annoying that Spectacles goes to fetch all dimensions and builds new queries every time it runs. If you've done a full run of Spectacles, have one small error and then fix that error, you want to quickly be able to re-test it. If you are confident that the dimension names themselves haven't changed (or been added or deleted), we should be able to use the cached results from the previous run.

Initially, I thought we would cache the dimensions, but I realise that I think we can actually just cache the query IDs themselves and then just re-run the query. That should skip the steps of finding the explores, finding the dimensions and building the queries, which would make it much faster.

If you were to add or delete a dimension, this option wouldn't work. I don't think there is a nice solution that lets you indicate which explores you want to use the cache for. If someone was in this position, I think they could just use the model/explore selector (as defined in issue #21).