LemurProto version 1.12.0

Usability improvements and the new Selector and Spinner controls.

Change log:

• Added SelectionModel.createSelectionReference() for obtaining a VersionedReference
  of just the single-selection state.
• Fixed DefaultCellRenderer to use 'null' as the default style instead of "root".
  This fits the overall API better and was probably a hold over from before there
  were default styles. It still might be a breaking change for someone.
• Fixed a bug where ListBox click listeners weren't getting executed.
• Added a Selector GUI element for selecting options for a list of values.
  Basically it's a single value field that pops up a list box when clicked.
• Added ColorChooser.set/getColor() that can be used to more conveniently access
  the edited color.
• Added ValueRender and a default implemenation DefaultValueRenderer that are
  more general non-list-specific value renderers similar to ListBox's cell
  renderer.
• Added ValueRenders which provides convenience factories for common value renderer
  use-cases.
• Updated CellRenderer to extend ValueRenderer.
• Modified ListBox to take a ValueRender to be more general. Since method
  signatures have changes this will be a breaking change for any ListBox-using
  code that cannot be recompiled.
• Added a SequenceModel interface and some default implementations to represent
  a potentially unbounded sequence of values that can be navigated forwards
  or backwards.
• Added a Spinner GUI element that allows next/previous through a SequenceModel
  as well as (optionally) direct entering a value.
• Added a ListBox.getSelectedItem() convenience method for retrieving the single-selection
  item in the list box.