Throw a helpful exception when nar.properties was not found

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add SCIFIO as a dependency

The ultimate goal of this demonstration is to use the Avian VM to
start a minimal Java Virtual Machine so that SCIFIO can be called to
read images for use in VIGRA.

For the moment, we rely on the SNAPSHOT version because of a crucial
bug fix (https://github.com/scifio/scifio/commit/1b2f9742) without
which the ImgOpener does not work with our custom ImgFactory.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Change the example so it loads /tmp/img.png

This is the next step: now we can already load a sample .png into
VIGRA-backed data structures via SCIFIO.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add support to export (save) VIGRA images

This will be useful for pure non-GUI testing, i.e. testing with Avian VM
(which does not come with support for AWT or any other GUI).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Save the image instead of displaying it

Rather than displaying the image -- which requires graphical abilities
Avian VM does not provide -- let's instead export the loaded VIGRA
image into a .tiff file.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Start describing how to run things in Avian

This does not work yet, but it is a start to find out what Avian VM's
classpath library is still missing, and adding the bits one by one.

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