EZP-21846: Contact form using symfony

Link: https://jira.ez.no/browse/EZP-21846

## Description
Information collectors have not been implemented on 5.x. So for now, the DemoBundle displays a way to build a contact form using the Symfony form and to send an email using swiftmailer.

## Tests
Manual tests

## Screenshot
![feedbackform](https://f.cloud.github.com/assets/4035241/2418939/fe37ec22-ab52-11e3-9985-eaa0fe21e843.png)




## TODO
- [x] Form controller
- [x] General cleanup
- [x] Finish html/css
- [x] Rebase commits