Admin screens

References:
* https://www.pivotaltracker.com/story/show/83500094

It became evident very quickly when adding features, that iHat needs visibility into the conversion process.  We need an easy way to see the overall status of iHat and identify and debug failures.

 This pull request creates some simple scaffolding to do the following:
* show paginated view of all jobs
* allow uploading epub directly from iHat that gets fed into the conversion process

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AC + CT
Unused block argument - `bower_rails`. You can omit the argument if you don't care about it.