Investigate changing our headless browser toolchain for Selenium

[Beak-man]

Selenium has many advantages over our current headless browser suite:

• It covers Safari and IE. We currently cover Firefox and Chrome only.
• Supports WebGL even in headless mode. I was able to render the Worldwindow with all its graphic elements to a .png in the command line (in Python, haven't tested it in npm).
• Very detailed UI events (mouse hovering, dragging, wheel scrolling) that can be performed programatically. It seems we could do all our functional testing for e.g. the examples with Selenium as part of our unit test coverage.
• The name is fitting for a NASA project :)

https://www.npmjs.com/package/selenium-webdriver