Trade interface improvements

[Kaballah]

Some things I'd like to see added to the trade interface to make it less unpleasant to use:
- Shift+drag left to buy all, Shift+drag right to sell all, for stacked items; Alt+click a field to zero it
- Ctrl+drag to buy/sell in large increments (e.g. 250 or 500)
- A slide bar filter for item damage, like on this alpha's workbench bill configuration pane
- A slide bar filter for item quality, like on this alpha's workbench bill configuration pane
- Items in the trade window are grouped in a treeview, similar to how they're already shown in the top left of the HUD

Stretch goals:
- A textbox entry field for number of units for stacked items, to allow you to just type in the amount you wish to trade (this is somewhat outside the current trade window's concepts because how do you determine which direction you're trading? I propose -5000 e.g.)
- A text item name search filter