Add a histogram widget to B&C dialog
Reuse existing HistogramBundle

While at it add a bunch of test code and a couple TODOs. They are related to
the lack of refreshing taking place when bouncing between two images.
minor code layout changes
HistogramBundle api now supports line drawing

The Brightness/Contrast plugin now draws an indicator line. To support
this there was some additional api added to HistogramBundle. And an old
constructor went away. This rippled through all commands that reference
HistogramBundles.
HistogramBundle api changes

Adopted IJ1's method for drawing slope line. Results are somewhat better
than before as aspect ratio maintained. The difference in contrast adjustment
between IJ1 and IJ2 is still very apparent.

While at it changed the name of getMin()/getMax() to getMinBin()/getMaxBin().
This rippled through into the Threshold command.
Add some code notes

This leaves in place original slope/intercept line draw code in comments.
Thus we can swap between the two methods if needed by a change in approach.
Fix changes tracking bug

While at it improve javadoc
Delete obsolete TODO
Merge branch 'bc-histogram'

This branch implements code that displays a histogram widget in the
brightness contrast dialog.