Add missing parent repository location
Split ImageJ service framework into scijava-common

This code was migrated and adapted from ImageJ:

    https://github.com/imagej/imagej

This new shared library will enable ImageJ and SCIFIO to have a common
base for plugin extensibility.
AppUtils: remove ImageJ-specific code

Specifically, the AppUtils.getBaseDirectory() method has been replaced
with:

  AppUtils.getBaseDirectory(String sysProp,
    Class<?> c, String baseSubdirectory)

And a simplified imagej.util.AppUtils#getBaseDirectory() method calls it
with the proper arguments.