Tell user to comment out FORCE_SCRIPT_NAME setting if not needed

If CATMAID runs in a domain's root, the FORCE_SCRIPT_NAME setting is not needed.
In fact, it is problematic if left in, because it adds an extra slash in
redirects. This comment extends the comment about this setting in the sample
configuration.
Let settings init script handle FORCE_SCRIPT_NAME properly

If CATMAID doesn't live in a subdirectory, Django's FORCE_SCRIPT_NAME setting
needs to be commented out. Otherwise, it leads to added slashes in a redirect
response. This commit makes sure this happens if Django's settings are created
with the help of the create_configuration.py script.