Responsive layout for better experience on mobile devices

[Dunedan]

This commit changes the layout of binder to provide a better experience on mobile devices and for form validation errors. It's outcome might not be perfect yet, but I believe it's a really nice step forward.

The changes consist of:

• moving the menu from the left side to the top, so it doesn't consume additional screen space when scrolling down
• changed the width of the content to depend on the screen size. For larger screens the forms won't consume the whole width, but validation errors will be shown beside the form field containing the error
• showing field independent error messages on top of each form
• highlighting of form fields which contain errors