Allow passing data arguments to a modal

Created by: kynan

Allows adding custom data as any number of data parameters:

<li><a data-person="Zim" data-toggle="modal" data-target="#person-modal"></a></li>
<li><a data-person="Dib" data-toggle="modal" data-target="#person-modal"></a></li>
...

Use the show event to inject your custom data into the modal.

    $('#person-modal').on('show', function (event) {
        name = $(this).data('modal').options.person
        $(this).find('.person').html(name)
    })

Implements a suggestion from @bronson in #531 (closed). Resubmission of #5261 with @fat's objections (hopefully) resolved.