Support Stopping Download

[HawkXP71 139]

Separating the enhancements out from Limit concurrent downloads (mobile app)

there are times when I dont want to "remove a download" but I want to stop a particular item from downloading.  

Adding a stop download, and force restart of download on an individual file basis, would likely also help with the "stuck in ready for transfer" that still seems prevalent based on posts and my experience.

I have found if the download dies midway, I have to clear the cache on the app (android) 

[Luke 43568]

Moved to feature requests.