Prevent the unit tests from opening a Java cup on MacOSX

On MacOSX, the unit tests which instantiate UI elements -- even if
they do not show them -- open a separate process with a separate dock
icon. This is pretty disruptive when developers run all the unit tests
in the background and try to do something else such as catching up
with their mail.

The apple.awt.UIElement property helps with that.

Suggested by David Philip Marshall in

	http://mid.gmane.org/1374227295612-5004030.post@n6.nabble.com

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Also suppress MacOSX dock icon in integration tests

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Unify IOPlugin implementations further

Following on from the last commit, this unifies the code style of each
of the three main IOPlugin implementations (for datasets, LUTs and text
files). It also actually guards against nulls for DatasetIOPlugin too,
which the previous commit did not.
Merge branch 'macosx-tests'

This suppresses the ugly Dock icon during unit and integration testing.

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