Add support for <exclusions>

The Bio-Formats release 5.0.0 unfortunately comes with incorrect
dependency declarations in its deployed .pom files. For example, testng
lacks the test scope and drags in a completely outdated xercesImpl
dependency that interferes e.g. with TrackMate when installed into
an ImageJ.app/jars/ directory (as noticed by Larry Lindsey).

Thankfully, Curtis Rueden added a work-around by putting appropriate
(huge) <exclusions> lists into the few projects' pom.xml files still
referencing Bio-Formats over SCIFIO (which does not sport incorrect
dependency declarations).

Let's teach MiniMaven about this, fixing
https://github.com/imagej/imagej/issues/33.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a regression test for the <exclusions> support

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