Implemented bulk email interface for new dashboard
disable buttons for large courses on legacy and beta instr dash

set max enrollment for downloads to 200
Implemented bulk email interface for new dashboard

Responses to Adam's comments; reset common.py, i18n compliance, deleted extraneous email.html file, fixed an HttpResponse, deleted unnecessary commented-out code, some small style tweaks
Changed GET to POST and xmodule HTML editor call, section CSS
Added acceptance tests for bulk email (through beta dashboard)
Merged in email confirmation modal
API tests, email tests, working notifications
added self to authors style, changed GET to POST
Legacy email tests, removed duplicate code, updated comments, fixed CSS
Removed email acceptance test
Revert remnants of disable-button, and how html editor is invoked.
Initial refactoring for bulk_email monitoring.
Add support for counting and reporting skips in background tasks.
Pass status into course_email for tracking retry status.
Refactor instructor_task tests, and add handling for general errors in bulk_email subtasks.
Factor out subtask-specific code into subtasks.py.
Move updates for InstructorTask into BaseInstructorTask abstract class.
Update handling of bulk-email retries to update InstructorTask before each retry.
Use HIGH_PRIORITY_QUEUE for send_course_email.
Add some handling for SES exceptions.