OZP-57: PortalPane base functionality
OZP-57: Refactoring common logic into superclasses and mixins
OZP-57: Widget panel collapse
OZP-57: Adding Portal sample data
OZP-57: PanelPane and PortalPane unit tests
OZP-57: Moving sortable behavior to PanelPane
OZP-57: Fixes to various panes
OZP-57: Fixing unit test errors resulting from merge