[FEATURE] Add unsupported browser message #584

Add message for old browsers like IE9 or (old) safari. This message is shown instant of the player.
resolve #584

I don't know whats a good and short Argument. I choose unsupported, because this takes effect on unsupported browsers. noVideoMessage or unsupportedBrowserMessage sounds even stupider and not remember able. 
To setContent without getContent i would need to add it in front of everything. I set the content after all attributes.