specify "content_type" rather than "mimetype" for JSON views

Something must have changed with the Django version  because
these views always worked before.
ddr-cmdln settings from [cmdln] section of ddr.cfg

The affected settings are currently used by ddr-cmdln rather than
ddr-local, or will soon be.  This change is in preparation for
moving ddrlocal.models.__init__.py code to the ddr-cmdln project.
ddrlocal.models now gets settings from ddr.cfg not settings.py

This is in preparation for moving ddrlocal.models.__init__.py
and associated files from ddr-local to the ddr-cmdln project.