[WIP] AIM Item Stacking

In Cataclysm's current state, displaying the item stacks only works for the player's inventory pane. This PR adds item stacking to the advanced inventory manager for all panes.

![2014-06-09 - 10_44_21pm](https://cloud.githubusercontent.com/assets/193401/3225178/d41a4dcc-f049-11e3-9439-ba02813e0e5d.png)

TODO:
- [x] get stacking working for single tiles
- [ ] port stacking code over to vehicle tiles
- [ ] figure out an implementation for 'ALL' pane
- [ ] code cleanup

Do we want 4 right-aligned columns (src, amount, weight, volume) for the 'ALL' selection? I'd be interested in people's feedback on this, as it'll truncate more item names in the display.