Initial change of logic for filtering enrollment list.
Merge branch 'develop' into feature/update_section_classlist_logic
Fix logic that returns enrollments that can be added to a section based on unique groupings of user_id and role that are not already present in the given section.  Tests to follow later.
Move role_key and new method to filter down enrollment list for adding to section into a separate "utils" module.  Modify section_class_list view code and tests to use this new utility.  Add new test class for utility method.  Updated/added method doc strings.
Merge branch 'develop' into feature/update_section_classlist_logic
Update section_class_list view method description.
Merge branch 'develop' into feature/update_section_classlist_logic
Merge pull request #85 from Harvard-University-iCommons/feature/update_section_classlist_logic

Feature/update section classlist logic