Make AbstractAnimator more re-usable

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
Add a TranslationAnimator

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
introduced additional abstract class AbstractTransformAnimator, such that
animators that do not provide an AffineTransform3D (TextOverlayAnimator) do
not have to implement this dummy functionality.
Revised comments and reformatted to imglib2 code style.
Make the HelpFrame re-usable for other help texts

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>