Install three different interceptors for opening files

It turned out that the previous approach was too limited (symptom:
when opening a cached sample, *two* images would appear). So let's
split the interceptor into three different ones: 1) File>Open,
2) IJ.openImage() and 3) File>Open Recent.

While at it, deprecate the old one (which is there only to make
imagej-legacy compile while we're switching to ij1-patcher 0.6.0).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge pull request #22 from imagej/intercept-open

Intercept file opening in more discernable ways