Add spectron for automated e2e testing

[develohpanda]

• Add spectron with a basic test Add spectron with basic tests #2531
• Run with installed app Add spectron with basic tests #2531
• Run with packaged app (after npm run app-package) Add spectron with basic tests #2531
• Run with built app (after npm run app-build) Add spectron with basic tests #2531 Build and package to a folder prefixed by the application id #2537
• Mock local server to query against Mock server for e2e tests using Prism #2544
• Add Core to PR pipeline Add e2e Core tests to PR workflow #2536
• Run tests specific to Core vs Designer Separate designer vs core e2e tests #2545
• Add Designer to PR pipeline Add designer smoke tests to CI #2549
• Add to Linux PR pipeline Add e2e Core tests to PR workflow #2536
• Add to Release pipeline - package and test
• Convert to ES6 style imports (investigate TS for the smoke-testing project)
• Update userData to set the app data directory - https://github.com/electron-userland/spectron/blob/master/test/commands-test.js#L214-L217