Move ImgLib1's sources to legacy-imglib1

All of imglib.jar's, imglib-ij.jar's, imglib-io.jar's and
imglib-algorithm.jar's sources are merged here with the intent of adding
ImgLib2-compatible wrappers for easier porting.

This is the next step in phasing out ImgLib1.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Start phasing out using imglib1

... by using legacy-imglib1 instead.

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