Updated Course ID Regex

This regex is nearly identical to the one used by LMS. The only difference is the internal capture groups have been replaced with character sets to avoid issues with the Swagger UI attempting to parse the internal capture groups and pass them along as arguments.
Added REST API for grade_distribution and sequential_open_distribution tables and test cases
Removed unnecessary db_column option parameterization from Model classes
Updated CSV filename

File names are now compatible with opaque keys.
Merge pull request #34 from edx/opaque-keys

Updated Course ID Regex and CSV filename
Merge pull request #35 from dylanrhodes/dylanrhodes/aggregate_data_apis

Added REST API for Grade Distribution and Sequential Open Distribution
Updated enrollment/gender endpoint to aggregate gender counts by day.
Merge pull request #36 from edx/dsjen/aggregate-genders

Updated enrollment/gender endpoint to aggregate gender counts by day.
Added Enrollment Mode
Moved Country Constants to Separate File
Merge pull request #37 from edx/enrollment-mode

Added Enrollment Mode
Education level returned as a string (rather than an education level object).
Merge pull request #38 from edx/dsjen/education-levels

Education level returned as a string.
Setting Default Values for Enrollment Modes

Defaulting to zero to avoid downstream issues with None values.
Updated Demographics and Enrollment Mode Serializers with Defaults

Both serializers will not return 0 if a demographic or mode field value is set to None.
Merge pull request #39 from edx/serializer-defaults

Updated Demographics and Enrollment Mode Serializers with Defaults
Merging Audit and Honor Enrollment Modes

The audit and honor enrollment modes are now combined into honor.
Upgraded to Django 1.7
Merge pull request #40 from edx/mode-merge

Merging Audit and Honor Enrollment Modes
Merge pull request #41 from edx/django-1.7

Upgraded to Django 1.7