Update rack-mobile-detect.

[Exoth]

rack-mobile-detect project seems to be abandoned, and its useragent parsing seems to cover much less mobile devices than Mobile-Detect regexps. I could do a fork of rack-mobile-detect and add there a Mobile-Detect patterns update task similar to the one in this project, but this is probably too much for a middleware. The fact is that I don't use its middleware capabilities, but I would like to have more precise mobile detection. Any thoughts on what we can do in this situation? We could add an alternative Mobile-Detect based is_mobile_device? method to mobile-fu, but having two methods with the same purpose looks somewhat strange.