Add SHOW_PROGRESS_SUCCESS_BUTTON feature

Show a button at the top of lms/templates/courseware/progress.html if the
lowest nonzero grade cutoff has been reached. Introduce two settings:
PROGRESS_SUCCESS_BUTTON_URL is the href of that button (the course id is
appended); PROGRESS_SUCCESS_BUTTON_TEXT is the text, defaults to
"Download your certificate"
Make the SHOW_PROGRESS_SUCCESS_BUTTON feature more flexible

The button text default is now in the template and i18n-able, a
PROGRESS_SUCCESS_BUTTON_TEXT_OVERRIDE option is offered in settings.
The button url now uses string formatting.
Add test in import code to make sure two overlapping courses aren't imported
Refactored terminology and added loop break for optimization
Switch PDF Textbooks to use portable URLs
install and set up paver before using it

install and set up paver before using it
install and set up paver before using it

install and set up paver before using it
Remove cruft from user profile threads

This removes the vote button from threads on the user profile, which was
the only interaction available on the page other than the link to view
the thread in the main discussion view.
Add pagination to forum user profile page
properly remove users from instructor/staff groups on a course delete
STUD-1555
Merge pull request #3304 from edx/zub/story/deletecoursegroups

properly remove users from instructor/staff groups on a course delete
Set initial video quality to large instead of default to avoid automatic switch to HD when iframe resizes. [BLD 981]
Separate each problem type into its own file

Separate all exercise and tool types, and create a new folder to contain them.
Merge pull request #3360 from edx/DOC-224

Doc 224
Merge pull request #3447 from edx/jmclaus/bugfix_hd_button_activates_by_itself

Set initial video quality to large instead of default to avoid automatic switch to HD when iframe resizes. [BLD 981]
Typo corrections
Merge pull request #3453 from edx/sylvia/docs/DOC-224

Typo corrections
DOC-115 adds topics to make data interpretation easier
Merge pull request #3287 from edx/ahodges/documentation/DOC115

Ahodges/documentation/doc115
Removed trailing periods in two scenario names