ManualTransformationEditor un/registers with SpimViewer as a Listener when de/activated.
Prepared support for transforming multiple sources simultaneously.
Use the new ImgPlus in imglib2 meta package

Signed-off-by: Jean-Yves Tinevez <tinevez@pasteur.fr>
ManualTransformationEditor: <ESC> aborts, <R> resets extra transform to identity
Merge branch 'transformed-source'

Conflicts:
	pom.xml
undo formatting changes