LUTFinder: use the context class loader

If we really limit the LUTFinder to the class loader that loaded
the class, we can neither add more .jar files later nor test
efficiently. Therefore: don't.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make sure that LUTFinder handles spaces in file names correctly

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