HistogramPlot limitations

The HistogramPlot plugin has its own UI code to support Swing and JFreeChart. It does not interact well with IJ2's menu display and program exit behavior.

For instance when selecting the hist plot window the menu only has the application submenu and no others.

Also if you exit IJ2 with hist plot win open the window will not automatically close. Instead IJ2 will not exit until you close the window by hand.

Perhaps we need to make the histogram plot a Display of some type. This should keep it from hammering menus and it should automatically close on program exit.

Migrated-From: http://trac.imagej.net/ticket/1854

Start by locating the HistogramPlot plugin's Swing and JFreeChart UI entry points, then inspect how its window interacts with IJ2 menus and application exit. Reproduce the missing menu items and blocked exit with the histogram window open. Done means the window integrates as an IJ2 Display or otherwise no longer disrupts menus and closes during program exit.

Written by the indexing model from the issue text.