Format the source code of the SampleImageUploader class

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
SampleImageUploader: warn when files >= 20M are about to be uploaded

This also gives the user a chance to opt out (if no user interface
is available, an error will be logged instead).

This fixes https://github.com/imagej/imagej/issues/40.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'sample-image-upload'

Some touch ups to the sample image uploader plugin.

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