Create functional tests

[hunterchristian]

• Use Spectron: https://electronjs.org/spectron
• Have functional tests execute as part of a nightly build. Do not have them execute as part of continuous integration, since the functional tests will run for a long time.
• Functional tests need to cover dragging an element from component palette and dropping them onto the canvas

[hunterchristian]

• Use https://www.npmjs.com/package/puppeteer-in-electron

• Relevant comment with puppeteer-in-electron conversation: https://github.com/puppeteer/puppeteer/issues/4655#issuecomment-519579145

• It's a small library. Source code: https://github.com/TrevorSundberg/puppeteer-in-electron/blob/d1794c257daa7b585f8f397352c8521f5ebd53c5/index.ts

• Need a workaround for drag and drop functionality. Currently broken in puppeteer. Conversation: https://github.com/puppeteer/puppeteer/issues/1265

• Workaround mention: https://github.com/puppeteer/puppeteer/issues/1265#issuecomment-419461871

• Workaround source: https://gist.github.com/vripoche/929ea5a5aff47cb0a68de92026939701

• Workaround summary: use the ability of puppeteer to evaluate javascript within a page to inject a script to drag and drop an element.

• Edit: skip the workaround and just trigger a drag/drop event using raw javascript