LegacyHooks: add intercept hook for dnd files

For future flexibility, it would be good to be able to intercept when IJ
is asking to open a file via drag-and-drop.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use SCIFIO when opening files via drag-n-drop

Tries using SCIFIO when given a File to open.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #23 from imagej/use-scifio-dnd

Use SCIFIO when opening files via drag-n-drop