Too heavy as a dependency

[chriswxyz]

Strongback is weighing in at nearly 1MB in consumer bundles. Let's aim for something far lower!

Some options:

• Reconsider what dependency libraries we're using
• Update to webpack 2.2 & es modules for better tree shaking

[chriswxyz]

js-joda is pretty big. What about https://github.com/date-fns/date-fns?