add initial user index implementation

just a list of users sorted by reputation
add gravatar to list
Merge branch 'master' into user-index
add reputation & pagination to list
fix issue where long usernames break page layout
Change UserController to use require_user for edit authorisation
increase spacing between elements
update gems
Merge branch 'user-index'
add link to user index in header
update gems
merge origin
Revert "merge origin"

This reverts commit e4e5642a0a977c519c66b7a1bb9ae81c02e85e63.
update rails
Merge branch 'master' into badges

Conflicts:
	app/models/user.rb
	db/schema.rb
	lib/jobs.rb