Ihat callbacks

### References: 
* https://www.pivotaltracker.com/story/show/83452714

### Heads up
* remove `IHatJob` model
* no longer make a subsequent request back to iHat to get converted file (just request it directly)

### DO NOT MERGE until iHat changes are pushed out


------------------
AC + CT
Line is too long. [124/120]