User merge - Githubissues

Adds new user profile partial to display user profile fields 🏑
Adds form to user show page to input dup user id if for merging 🦆
Controller to handle previewing and confirming user merge 🎁
Actual merging post-confirmation is not yet implemented, pending some work on errors in Northstar🎢
This is pretty much all Dave but I shall take the credit shamelessly :trollface:

DoSomething / aurora