Generate aggregate_tables for caching

[scholtzan]

It would be useful to generate aggregate_tables for caching data. This requires some more exploration of what the best way of doing this is. We will need to generate aggregate_tables for possible filter combinations but at the same time want to limit the number of aggregate_tables for filters that have a lot of different values.

This will require making dimensions available across views, explores and dashboards. An implementation already exists for operational monitoring, see also #295 (comment)