macosx: implemented full management of custom equalizer presets (refs #383)

create as many presets as you want based upon the respective current selection and remove any (including the defaults), if you don't like them. Reset VLC's preferences to get the original set back. There is no way to edit existing presets and this isn't scheduled for now.

NEWS

@@ -84,6 +84,8 @@ Mac OS X Interface:
  * add a GUI to capture QTSound data along with the current screen content
  * add an option to let the Apple Remote control the system volume instead of
    VLC's internal volume level
+ * add the ability to create custom equalizer presets based upon the current
+   selection and to manage the list of presets
  * add an option to disable skipping to next/previous file with the Apple Remote
  * add an option to show next / previous buttons
  * add an option to hide the shuffle and repeat buttons