v2.2.0

Features:

• Add public getters for left/right grids (#68, #31)
• Expose the component as a HasValue of List (#66)
• Preserve UI sort orders in getValue (#66)
• Implement addSortableColumn overload that sets the column key (#70)
• Deprecate the protected final leftGrid/rightGrid fields.
• Deprecate all the methods that just delegate into an equivalent call on the left/right grid.

Fixes:

• Return empty set in getEmptyValue (#72)