Hotfix/progress 500s

This PR fixes two 500 errors appearing on the progress page

1) When we create a module from a sequence with dynamic children, now we check to see if that module is None before asking for its child_descriptors. If None, we return an empty list.
https://edx-wiki.atlassian.net/browse/LMS-1039

2) The progress page broken when section titles with unicode was passed into it. This PR fixes that and generally updates the progress page to use unicode instead of strings.
https://edx-wiki.atlassian.net/browse/LMS-1093

3) Oh, and for bonus, makes the dev setting for DISABLE_START_DATES False, so that local student accounts look more like prod accounts. In staff mode, that flag is turned on automatically anyway.

@ormsbee 
@rocha