Refactor the "create" Order action

Previously, most of the logic that was required to create orders was contained in the orders controller, which was causing the action to become large and unmaintainable. The logic has been extracted from the action into separate classes.

https://trello.com/c/dgrFMz6o

![](http://www.reactiongifs.com/r/conga-line.gif)
Resolved in f338cba