Update dependencies, make any necessary changes

[nowthis]

Move to the newest versions of:

• d3
• canvg

[nowthis]

The Canvg version used by SankeyMATIC has been updated from 1.3 to version 3.0.9, as of commit 877aa705ebaf3e18b95b24b411bf87ad47c76b93 (This means that rgbcolor.js is no longer a required file; it is essentially embedded in the canvg package.)

Updating to the latest D3 version is coming someday relatively soon too.

[nowthis]

Currently updating SankeyMATIC's version of D3 from 2.x to 7.3.0 (the latest).

The changes included:

• Update the category color schemes to use the new named schemes
  • (The whole theme-picking interface is about to be overhauled after this change, so this is just an interim step..)
• Update the dragmove function to use the new event handler style
• Re-institute the individual calls to .attr, .style, etc.
  • The grouped style seems to have gone away sometime in the last 5 major versions.
• Adapt the .nest call inside sankey.js to a new Array map instead.

This change did not require adopting the latest d3-sankey module. There are some good ideas there, but the versions have diverged so much that I'm just sticking with my modifications. I might adapt some specific concepts they've added in the future.