Feature/190 more form validations

What does this MR do?

• Login page refactored to twig template.
• Login form refactored to symfony form.
• Login form javascript moved into new Login.js file, updated webpack config.
• Login javascript now uses 'match-media' rather than 'window.resize' (we could leave this out if you're worried about older browsers although support looks pretty good).
• Register form is now a twig template. I was a little apprehensive to refactor this to a symfony form just yet as it seems considerably more complicated and may make sense as a follow up MR that I make that can update the javascript too.
• New pages use the new translation system (there may be some duplication here that should be cleaned up). But in the interest of not breaking something relying on the old system, I've left it in place.
• Tests updated to reflect symfony form naming / data structure convention.

How confident are you it won't break things if deployed?

This will require quite a bit of testing due to some changes to how login is handled.

Links to related issues

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))