Add PNG Chart export

[ddohler]

Overview

Allows users to export charts as PNGs.

Demo

Notes

This is WiP until azavea/climate-change-components#51 is merged and a new version is released. After that happens, this should be updated to pull in the latest version in package.json, and remove the dependencies for SVG export and file saving. The TEMP: DO NOT MERGE commit also will need to be removed.

Testing Instructions

Either

• Check out the code from Add Export Services from Climate Change Lab climate-change-components#51 in your development environment for that project.
• In the CC components repo, run yarn run build:library
• Check out 03b3bcb and run vagrant up and then vagrant ssh and scripts/update
• Check out b6051ef and run vagrant reload

Or

• Follow these instructions to pull in a copy of the climate-change-components repo: Use distance parameter for climate API calls #1179

Then

• vagrant ssh and then scripts/updated followed by scripts/server
• Either way, then vagrant ssh and scripts/server
• Load up the app, and click on every graph you can find and make sure that there is 1) A Download button 2) That the download button works and 3) That it downloads a valid PNG that reflects the chart.

• Is the CHANGELOG.md updated with any relevant additions, changes, fixes or removals following the format of keepachangelog?

Closes #1171

[ddohler]

This has been updated and is ready for review.

[maurizi]

Is the border around the section the Download button is in an intentional design decision?
It feels like a styling bug to me:

[maurizi]

These imports are making the linter unhappy (need to be aphabetized)

[ddohler]

Good call on the border; it never really registered as a problem for me (but I totally see what you mean), but when I looked into it, it was because of a directive that had snuck into the HTML that was no longer necessary in Temperate, so I took it out.