Keep history of tallies [untested] [WIP]

* Change format of tallies file to keep previous tallies
* Done offline => untested
* Work in progress: Display needs to be updated as well
Follow-up: Adapt code/display for temporal series
Change metric to be less strict

* If we have a machine-readable license URL *or* a license name, we're good.
* If we have a description *or* an author *or* a source, then the data is probably machine-readable, and if stuff is missing it's missing in the field. That's a different problem that can be addressed with CommonsMetadata's new tracking categories.