It’s invalid HTML to have multiple labels nested within each other. This
was happening by accident because WTForms tries to be clever – when you
put `{{ field.label }}` in a template it prints a `<label>` tag for you,
not just the text of the label. But we put our own `<label>` tags in the
HTML to have more control of them.
This commit stops WTForms being so clever.
The yes/no pattern didn’t work too well, because:
- it didn’t read naturally as a question and answer
- often users left them completely unclicked if they didn’t want to set
the permission (rather than clicking no)
This commit changes both the invite and edit user pages to use
checkboxes to set permissions. If also rewords these pages to read more
naturally, and explain what the permissions mean.
This meant changing some of the view logic around invites and
persmissions, and I ended up refactoring a bunch of it because I found
it hard to understand what was going on.
