Refactored mixins into utils
ES2015 module exports
ES2015-style imports
WIP Fixing tests
Fixes tests after es2015 code migrations.
We we're require()ing an ES2015 module[1]. Have to make sure you account
for the .default in this case.
[1] We had to use ES5 `require` in Jest:
(https://github.com/babel/babel-jest/issues/16)