Use advancedsetting to speed up ReadRate of players

This is the follow up of the discussion here: https://github.com/xbmc/xbmc/pull/2901

The limits for the advancedsetting were removed also after discussion was (1.0 .. 4.0 before). I hope we can end the famous cache talks with this PR.

Thanks to all that did contribute to the discussion in a technical mannor.

@elupus: Your green button