Fix itemcases not being able to use some items (Fixes ItemCase-1)

ItemCases are unable to use items like Saplings, grass and flowers because the event action is defined as "LEFT_CLICK_AIR".
Fix formatting of prices (Fixes ItemCase-2)

The prices displayed are not properly formatted for currency.
Fix the selling price being the buy price (Fixes ItemCase-3)

The sell price given to the player is actually the buy price.
Add indication of UI buttons (Adds ItemCase-4)

Add indication of the UI buttons to players as most are unaware and think they have to type the commands.