ARL_ExpWhateverOptCB are all now MainPanel.menu_toggle_whatever

ARL_ExpWhateverOptCB are all now MainPanel.menu_toggle_whatever
ShowFilterMenu() has been completely re-written and now exists as MainPanel:HighlightCategory(), and now hides the filter menu if no parameter is given.
ToggleFilterMenu() now uses category names instead of numbers.
CreateFilterMenuButton() no longer has a button name parameter and will no longer name the textures it creates.
Renamed ExpButtonText to CATEGORY_TEXT, and changed it to a dictionary table.
Renamed ExpButtonTT to CATEGORY_TOOLTIP, and changed it to a dictionary table.
Removed some unnecessary comments.