[push] Display upload progress to user

[rufuspollock]

At the moment, when pushing packages, especially big ones, it is not clear what's happening. We want to have a progress bar so users know which stage is being processed.

Acceptance criteria

• When I do push, I can see the progress of upload process

Tasks

• refactor push method of DataHub class in datahub-client library
  • add a listener for formData and implement it along with the progress bar
• refactor data-cli library to work with it

Analysis

We will use progress npm package to implement the progress bar - https://www.npmjs.com/package/progress

See example here https://github.com/visionmedia/node-progress/blob/master/examples/download.js

Using the example above, implement progress bar here - https://github.com/datahq/datahub-cli/blob/master/lib/utils/datahub.js#L49-L82
Use totalLength for total parameter.

Not sure if we can use fetch here: JakeChampion/fetch#89

[anuveyatsu]

FIXED - will be available in release >v0.8.2