Fix various UI bugs
- Introduce UIComponent.mouseMode to figure if a mouse should cross a UI to intersect with the scene
- Fix possible problems with scrollbars (drag ‘nd drop)
- Fix storage bug, moving when transferring items
- Fix css bugs on UI drag ‘nd drop
Fix background problem (full black sometimes)
Rewrite public/private access to variables and methods.
Various UI clean up
- add UIComponent.focus() to clean up some part of the code
- Fix UI drag/drop problem
- remove useless code (because of the drag/drop change)
Massive UI clean up
- Clean up closure function.
- Fix problem with drag drop and buttons.
- Fix draggable elements (match the official UI).
- Fix guild markers on minimap.
- Fix possible memory leak (keydown could be set multiple times).
- Fix trade UI, conclude button should be enabled just when the two players validated the trade.
- Trying to fix the Firefox mouse intersection bug (mouseleave + remove problem, test case: http://jsfiddle.net/7h4sj/)
- Fix possible problem with resizing UI.
Display discount price on NPC Store
Fix firefox appendChild/scroll problem
On firefox ```appendChild(element)``` reset the element scrolls position, implement a new way based on zIndex (more complicate, but do the job).
Merge pull request #67 from vthibault/various-ui-fix

UI Improvement
Fix a lot of UI problems (drag/drop, scene intersection, scroll problem)