Category Select Mode for Inventory, Advanced Inventory and Multidrop Windows.

This PR adds a category select mode to the inventory, advanced inventory and multidrop windows. [SPACE] toggles between the original item and the new category selection modes. In category select mode, the UP/DOWN arrows jump the selection to the first item in the next/previous category of items. Item selection mode is the default mode when the windows are opened, and is the same selection mode that everyone is already used to (UP/DOWN arrows move the selection a single item at a time).

Pictures speak a thousand words, so how many do an animation speak?

![cataclysm_category_select_inv](https://f.cloud.github.com/assets/6007524/1680300/86eed4b0-5d72-11e3-883e-420ef04e2292.gif)