* store prefill params in session
Instead of using query params on /dossier/new, we assume the user comes
from /commencer/:path, which is the new prefill link.
There, we store the prefill params in session, and use them to prefill
the dossier when creating it, in /dossiers/new.
* spec: cover the case
* review: serialize with json instead of yaml
* review: rename method
* review: store only query params
* review: comment why we dont override already stored params
Test helpers are separated between two files: spec_helper and
rails_helper. This separation is meant to allow tests that do not
require Rails (like testing standalone libs) to boot faster.
The spec_helper file is always loaded, through `--require spec_helper`
in the `.rspec` config file. When needed, the rails_helper file is
expected to be required manually.
This is fine, but:
- Many test files have a redundant `require 'spec_helper'` line;
- Many test files should require `rails_helper`, but don't.
Not requiring `rails_helper` will cause the Rails-concerned section of
the test environment not to be configured–which may cause subtle bugs
(like the test database not being properly initialized).
Moreover, Spring loads all the Rails files on preloading anyway. So the
gains from using only `spec_helper` are thin.
To streamline this process, this commit:
- Configures `.rspec` to require `rails_helper` by default;
- Remove all manual requires to spec_helper or rails_helper.
Reference: https://stackoverflow.com/questions/24145329/how-is-spec-rails-helper-rb-different-from-spec-spec-helper-rb-do-i-need-it
