add static methods to find extrema values in an ImagePlus and to optimize the display range
Create new plugin to do marker-controlled watershed.

This plugin replaces the former one with the same name. The difference is the new plugin doesn't look for regional minima. The user needs to introduce the labeled makers.
make use of new method to optimize the display range of the result
For consistency, use the Watershed3DPlugin to call the classic watershed method (no markers)
add static method to call the classic watershed on a input image with optional mask
add methods to perform classic watershed using a binary mask to restrict the region of interest
add new plugin in the configuration file