3D Objects Counter: be less impolite

Given how usage varies among different parts of ImageJ and the Plugins, this
message is really rude and annyoing. Just be informative instead.
Merge branch '3d-objects-counter' of https://github.com/imcf/fiji

This makes the 3D Objects Counter less rude.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>