User <-> Proof association

Failures:

  1) Manage proofs user views all standards and proofs
     Failure/Error: expect(page).to have_css '[data-role="proof"]',
text: user.proof.image_url
     NoMethodError:
       undefined method `proof' for #<User:0x007fecc72ec848>
     # ./spec/features/manage_requirements_spec.rb:28:in `block (2
levels) in <top (required)>'

Finished in 0.19701 seconds
1 example, 1 failure

Failed examples:

rspec ./spec/features/manage_requirements_spec.rb:20 # Manage proofs
user views all standards and proofs