WIP on showing histograms in plugin UIs
Improve HistogramBundle min/max calcs
Fix HistogramPlot errors
Update histogram chart when histogram changed
Do not cache widget label

Some controls (like buttons) can change their label at runtime
Allow button labels to change dynamically
Allow messages to change dynamically
HistogramPlot no longer swing-based

It now uses pure IJ2 @Parameters and a HistogramBundle. The graph is created
elsewhere in the widget logic.
Move HistogramPlot out of swing commands

HistogramPlot no longer depends upon Swing. Yay!
Fix button mutating bug
Fix numeric panel initialization bug
Merge branch 'histogram-widgets'

This merge adds histogram widget support to IJ2 and utilizes them in the
histogram plot and threshold commands.