Users can create pitches for journalists

Trello: https://trello.com/c/0oul2GrI/44-users-create-pitches

In this feature, users can create write one pitch, assign multiple journalists and have an individual pitch created for each journalist.

I suspect the batch_pitch_params part of the batch_pitch controller can be refactored.

Includes addition of pry & better_errors gems
I didn't feel awesome about having a each do loop in my controller... I felt as if I was asking the controller to do too much. I agree with the instance variables being a smell though, so I suppose the better solution is to keep this in the controller.