- Use URL.createObjectURL (replace from FileReader)
- Use HTMLCanvasElement.prototype.toBlob
(replace from HTMLCanvasElement.prototype.toDataURL)
- Use Promise (replace callback interface)
* Add eslint-plugin-promise to detect uncaught rejections
* Move alert generation for errors to actions/alert
* Add missing rejection handling for Promises
* Use catch() instead of onReject on then()
Then it will catches rejection from onFulfilled. This detection can be
disabled by `allowThen` option, though.
