merge in data documentation, data downloader updates

[bucketteOfIvy]

Merge in the changes to the data documentation and data download tabs. These include:

• Data documentation page now points to updated metadata, only points to rows with metadata, displays updated source(s) and years, and follows the modern organization/theming from the data dictionary
• Data download page now allows for download of full v1.0 repository or for downloading subsets (or all of) the version 2.0 data

Both sets of changes were accomplished in-part by pointing to the most up-to-date version of the GeoDaCenter/opioid-policy-scan repo, meaning that changes to the organization of that repo might break something. As such, when v2.0 of that repo is released, the links on line 11 of explorer/pages/docs/[md].js and line 60 of explorer/download.js should be updated to point to the static links.

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