Support sorting of game list via input

You can now map the functions "sortordernext" and "sortorderprevious" to
inputs (in es_input.cfg) and toggle the game list sort order with them.
The order is: "file name, ascending" (default), "file name, descending",
"rating ascending", "rating descending", "user rating ascending", "user
rating descending", "time played ascending", "times played descending",
"last played time ascending", "last played time descending".