refactors gulp using rollup

[UncleGedd]

Refactors Gulp, issue # 67

I have done this work using both Webpack and Rollup, and Rollup is by far the easier solution both in terms of setup and extensibility IMO. Also, Rollup is created specifically for the purpose of building flat libraries, whereas Webpack has many bells and whistles that make it quite complex to set up but great for web apps.

• Refactors build tooling using Rollup (went from a 192-line gulpfile.js to a 61-line rollup.config.js
• Modifies npm pretest hook
• Adds mocha and eslint (non-Gulp versions)
• Removes Gulp and other dev dependencies (composer, del, uglify-es)
• Regenerated package-lock.json
• Adds babel transpiling during builds (see this comment from PR # 70

[poorejc]

Merged earlier PRs, but want to test the new build pipeline on updated test branch. Will test and review tomorrow thanks again @UncleGedd

[UncleGedd]

Just rebased from master pulling in the cypress journey changes and resolved the resulting conflicts