Includes management command and instructor dashboard button which gather all open assessment response data for a given course in a user friendly format and output it as a .csv

WIP finished collect_ora2_data management command, wired it to instructor dashboard UI, still needs to have logic factored out and exposed in instructor_analytics.basic

Remove extraneous print statement

Refactored sql querying logic into instructor.utils and wired the html button and management command to it there

Added comments to several methods

Added optional output_dir argument to collect_ora2_data management command and default behavior to write to stdout

Simplified code structure in management command and comments per jrbl's PR comments

Responded to jrbl's style comments, added test reference to check endpoint, and parameterized database name from django.conf.settings

Removed reference to django.conf.settings['DATABASE'] in favor of django's natural default

Removed extraneous import and whitespace per overlooked jrbl comment

Factored db connection logic into common/djangoapps/util/query.py

Whitespace changes
Merge pull request #136 from Stanford-Online/dylanrhodes/ora2_instructor_button

Ora2 aggregated data download button and management command