HTMLHiddenField is unable to output a non-default value, which makes it
unsuitable for actually persisting changes across multiple form
submissions. To preserve compatibility with forms that aren't expecting
persistence, fixing this requires a new parameter in the field
definition.
Also, due to the unusual way that hidden fields are added to the HTML
output, they are not being correctly handled by HTMLFormFieldCloner.
Special-case that.
Change-Id: I1fde7372401299b4432d28ac61982d47d5f3bbea
SecurePoll is going to need the ability to have a form for stuff like
"one or more admin usernames" and "one or more poll questions, each with
one or more options".
This change implements a generic field container that simply displays as
a <ul> followed by an "add more" button, with each <li> containing
various fields including a "remove" button.
Since this is only going to show up in SecurePoll to people creating a
poll (not to general users), the current design is functional but not
necessarily beautiful. Those interested in beauty are welcome to do so
in a followup change.
Change-Id: I46fad3971739ddc961259fe32eb6e1cd265a1c06
