Updates specs to use new rails5 format.

The old format:
`get :show, { some: params }, { some: headers }`

The new format:
`get :show, params: { some: params }, headers: { some: headers }`

When a user checks the `accept` checkbox, we will track that
acceptance as usual. That way they don't need to accept again after
they complete the registration.

When an unauthenticated user visits the `/-/users/terms` page, there
is no button to accept, decline or continue. The 'current-user menu'
is also hidden from the top bar.

Signed-off-by: NRémy Coutable <remy@rymai.me>

If a user presses the 'Register' button too quickly after attempting
to solve the reCAPTCHA, or the reCAPTCHA is not solved at all, the
user would experience a 500 error. Now, the case is properly
handled and the user will be sent back to the registration page
with a clear error message and can try again.

- Look for a `change` in its size rather than asserting against an
  actual size.

- This previously failed because another spec had an email in
  `ActionMailer::Base.deliveries`, which failed this `be_nil` assertion.

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Also removes the note from the development/testing.md guide