Enhancement: IFrame widget to be able to receive URL from String item

[kubawolanin]

This one is in fact similar to #19. Current iFrame widget allows you to display any website from a given URL passed in the widget settings. It would be great if we could choose whether we want to:

• Get the URL from given String item in openHAB
• Type the url into config text

My use case scenario: I have a rule that reacts on my voice command. If the command contains some specific keywords, my HABPanel should be set to specific dashboard and set the URL of an iFrame dynamically. e.g.

rule "Show me the timetables"
when
    Item VoiceCommand received command
then
    if (command.contains("how can I get to the central station")) {
        habpanel.postUpdate("timetables") // set the dashboard
        myIframe.postUpdate("http://timetables.example/?from=MYHOME&to=Central+Station")
    }
end

Hope that makes sense! :)

[kubawolanin]

FYI: Started working on that feature on feature-98 branch ;)