Add support for d3 rather than Flot

Please consider using something with d3, not Flot. Flot was probably the best choice for this at some point, but as an open-source project it didn't feel healthy last time we evaluated it. We are still using it in our services (see signature), but are going to replace it.

from Sematext.

Start by locating the existing Flot integration in the repository and reviewing how charts are used by the faceted-search front end. Determine the scope of replacing Flot with d3; done should mean the relevant charts work with d3 and the old Flot dependency or integration is no longer required.

Written by the indexing model from the issue text.