Merge pull request #9 from gorchov/progress-tracking

Progress tracking
add basic destroy test for lesson completions controller and pass it
refactor existing actions to use the before_filter authentication
finish up basic controller tests for lesson_completion deletes and tweak routes
refactor to replace references to student with current_user
switch to delegated event listeners and wire up the 'not completed' link to the back end
fix link to logged_out svg image
alter test description to match convention for alerting to JS tests (which fail on nitrous right now)
slight refactoring to remove redundant student_id attribute since controller doesn't need it