initial commit
fixed checkboxes' read-only state

unfortunately, `readonly` doesn't actually work for checkboxes, as it
only applies to fields' *value*, whereas we're interested in *state*:
http://stackoverflow.com/a/155301

so we have to use `disabled` instead - the consequence that values are
not being transmitted to the server should be of no consequence in this
context, as these checkboxes should never end up in a form