Port LLK/scratchr2#4168 for ScratchX.
Original description from that change:
> This fixes #4112 by creating the swf regardless of OS and browser.
> Calling `embedSWF` would first check for the existence of the plugin
> before creating, causing browsers that don’t allow the flash plugin by
> default to not be able to show their “allow” message. This tries to
> create the swf no matter what, allowing browsers to detect flash
> Logic is as follows:
> 1. check if `userAgent` returns a mobile/tablet OS. Display error
> message if so
> 2. check if on windows and using ie – check for an express install if
> so (like in `embedSWF`)
> 3. load the swf in all other cases, let browsers handle it.
> Test Cases:
> - Test how project pages load in Android and iOS devices, on tablets
> and on phones, and on multiple desktop OS's for correct loading
This resolves LLK/scratchx#103