Incremental update mechanism for images

Some tools need a mechanism to iteratively update and redraw images at a rapid rate. E.g., the fitting process in the [SLIM Curve plugin](http://fiji.sc/SLIM_Curve) is very slow so there is a scheme to refresh the fitted image incrementally so that progress and results may be monitored.

It would be useful to generalize this somehow in the IJ2 framework.

Migrated-From: http://trac.imagej.net/ticket/1748

Start by reviewing the IJ2 framework's existing image update and redraw mechanisms, then compare them with the incremental refresh scheme described for the SLIM Curve plugin. Define the reusable API and its completion criteria before implementation, since the issue does not name files, tests, or a specific design.

Written by the indexing model from the issue text.