Add drawnow to unmanage function to ensure everything is up-to-date

This commit includes a number of changes which are tracked elsewhere:

Bug Fixes:
 - Fixed the ColorbarVisible property, which in turn enables the toolbar button in the figure window.
 - Fixed behavior of custom set colormaps when saving to and loading from .fig files.
 - Fixed ksdensity option for DensityMethod property
 - Added extrapolation logic for the binned DenistyMethod to ensure that all points get assigned a color/alpha.

Features:
 - Added XLabel, YLabel, and ColorbarLabel properties.
 - Added an unmanage method which converts the chart into 'traditional' MATLAB graphics objects for advanced editing.
 - Moved property help to a linked static method.

Update README to fix image link