Added misc settings panel + option to rm alphabet overlay

Added a miscellaneous settings panel which might get populated as the
skin evolves.

Right now it contains the newly added option to remove the alphabet
overlay when scrolling media.
Rename dialogslider so that the skin can't use it as it crashes xbmc atm

As soon as the slider is called (e.g. manually syncing audio) xbmc crashes, removing or renaming this file fixes crashing and doesn't remove any functionality
Undid last commit will redo this after previous PR
Added option to disable alphabet overlay when scrolling to the new section "Visuals"

Last PR was rejected for "The option could be included in the Visuals section of the settings window - no need for a Miscellaneous section."

So included it in the new visuals section
Merge pull request #60 from hessius/master

Added option to rm alphabet overlay to Visuals