WIP: implement LegacyImageDisplayViewer
TEMP: update to ij1-patcher 0.4.3-SNAPSHOT
Update packages for 0.4.0

The imagej.legacy package is now net.imagej.legacy for consistency.
Updated all imports to match the new package structure.
Add a plugin type to intercept ImageJ 1.x' opening images

This plugin type will need to be implemented by all plugins wanting
to have a say how an image is opened.

It is our design to improve on HandleExtraFileTypes; Now developers
can extend ImageJ 1.x' image opening without stepping on each others
toes, badly.

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