Preserve smooth row-by-row scrolling for mouse wheel input, but restore
full-page movement for controller/menu scroll actions in the creative
inventory.
Commit 3093ca3 changed page indexing to support smooth scrolling, which
caused ACTION_MENU_OTHER_STICK_UP/DOWN to advance by one row instead of
one page. Track whether the scroll action originated from the mouse
wheel and only use single-row steps in that case.
Fixes#253
7b35df8714