Front-end: Better forms

[joachimesque]

Some fixes and enhancements for many forms.

• Use class="field" when possible for more consistent spacing between form fields
• Only allow input[type="checkbox"] or input[type="checkbox"] inside <label>
• Truncate file URL in clearable_file_input
• Place checkboxes and radios before label text
• Disallow interactive elments (like a) inside label

[mouse-reeve]

this is such a big improvement! thank you!