#609 Add ability to set "next/previous chapter" in mouse functions

[ShinoK]

Please add the ability to set "Next Chapter and Previous Chapter" in the side buttons of the mouse ( "X Button 1 and X button 2" ) as it's now missing.
While it can be done in the Main Toolbar,having to exit full screen mode to switch chapter is not a nice way to do it.

[Ricardo Villalba]

Done in svn r6765.