Remove Blink dependency

[halleysfifthinc]

Disclaimer: This PR is not-entirely-serious, and is mostly intended to start a discussion.

Blink is a large dependency with a correspondingly large load time (@time using Blink # 2.42 seconds on my PC).

There are two major benefits from removing Blink as a dependency:

• Faster load times.
  • @time using PlotlyJS drops from 3.12 to 1.02 seconds, with matching decreases in number of allocations and total allocated memory.
• Reduced direct and transitive dependencies.
  • In particular, without Blink, there is no transitive dependency on WebSockets, which is incompatible with new(er) versions of HTTP > v1. The presence of WebSockets in the environment downgrades HTTP and any packages/versions depending on recent versions of HTTP, which is particularly inconvenient in large environments (which despite recommendations to the contrary, are the norm from what I can tell).

Some relevant questions:

• How many users depend on the Blink functionality vs using Jupyter?
• Do the number of Blink users justify a 3x loading time?
• Could we split this out into a separate package?

(Fixes #272)

[jd-foster]

I think this function is used when generating the Documenter pages (not for Blink per se).

[jd-foster]

There could be an argument here for a weak dependency version too as in #463 .