Settings: use subdirs of MEDIA_ROOT for output in HDF5 and cropping tools
Settings: make settings generator Python 3 compatible
Settings: let the settings generator replace douple-slashes

Double-slashes will occur in the generated settings files when CATMAID
lives not in a sub-directery, but the domain's root.
Settings: use correct import URL placeholders in settings templates
Settings: let the settings generator create a secret key for Django
Settings: update the setting generator template file
Settings: add leading/trailing slash checks to settings generator
Settings: rename settings_apache.py to settings_production.py