improve digilib url parameterization

[bwbohl]

e.g. on build in build.properties and build.properties.local
or even better in some prefs.xml

[riedde]

If we try to link the sourceImageCartographer to the ediromBackend (which we should develop further!) that it would be easy to get the preferences. In that case we could also store the image-prefix as parameter and just request it.
But this solution would be some kind of integration or joining of the two apps.

[bwbohl]

This could also be managed dynamically e.g. by looking for the other package before swiching to a supplied parameter, before switching to a default value.

[nikobeer]

This would be a nice feature! I am open for any solution.