New panel manager (epic)

[davebalmer]

Automagic multi-column stack manager. Used to make the UI more responsive to wider screen formats, or revert back to standard stack behavior when there is not enough room to make columns (generally, in a portrait orientation).

Features:

• Creates multi-columns on-demand; each column is a stack inside of a hierarchy
• If there's not enough room for the next column, the manager should make room by shrinking the current left-most panel (or more as needed)
• Developer should be able to set the min/max panel size, and maximum number of panels
• Should work with global back gesture (also: back buttons should fire this gesture; make another issue for this)
• Interface similar to joStack/joStackScroller
• Should allow additional parameter (possibly on push()) which indicates if the app desires to push out to a new column
• Should allow the end user to expand/compress panels

Either will consume joStackScrollers, or extend it. Probably consume...