Merge pull request #1 from almende/develop

Sync with upstream
Merge pull request #2 from almende/develop

Merge in upstream changes
Halfway rebuilding ItemBox without dynamic reflow
Stacking starts to work
Cleaned up redundant code
Moved some variables from ItemBox to Item
A fix in updating the visible items
Merge branch 'develop' into simplified
Rewritten ItemRange
Merge branch 'develop' into simplified
Refactored ItemPoint
Refactored ItemRangeOverflow
Made Item.isVisible independent of parent
Refactored item selection
Temporarily fixed stacking in a primitive way
Refactored Itemset.repaint, simplified vertical positioning of items
Merge branch 'develop' into simplified
Simplified TimeAxis
Removed reflow step from Panel, RootPanel, and ContentPanel
Halfway reworking the GroupSet