* Make modals display in source Window
this makes modals display within the window where they got opened, with the parameter `rootwindow` that, if `yes` or `true`, shows the modal always in the root TW window (`<$action-sendmessage $message="tm-modal" $param="mymodal" rootwindow="yes|true"/>`)
* pass the full event to $tw.modal.display
we need the event there to find `srcDocument` and `srcWindow`
* pass event in options object
* update modal.js to use options.event
* add docs for rootwindow tm-modal attribute
@felixhayashi I’m afraid I haven’t used your pull request as there were
a few details that I wanted to do differently. The main change is that
these changes allow both a param string and hashmap to be specified.
