TNL-670

TNL-649

visual indentation

This commit adds validation for course advanced settings. Currently when course
administrators make invalid changes in the Settings/Advanced Settings tab,
they're not notified through a new modal window of the list of invalid settings
changes.

* Extending CourseMetadata
    - Previously, we only had update_from_json method in CourseMetadata.py,
      and it was only validating one field every POST request.
    - Now we have validate_and_update_from_json method that encapsulates the
      functionality of update_from_json into a validation call
    - To avoid discrepancy of validation standards between modules, validation
      uses the from_json method implemented to each field in xblock.

* Different Response in advanced settings ajax requests
    - After receiving a POST ajax request, course.py calls
      validate_and_update_from_json, and sends a json object of either:
        1) valid course metadata model
        2) error objects

* Error Messages shown in validation-error-modal
    - error objects passed through ajax are shown in a separate modal.

BLD-1207

STUD-1875

The fields should be translated before render into html templates.

Refactor get_parent_locations STUD-1663

STUD-302, STUD-303

with code to translate between addressing schemes based on app
and persistence layer addressing scheme specification.

STUD-1206

[LMS-1614]

STUD-948

Hide show_timezone from Advanced Settings and migrate courses with show_timezone=False to using due_date_display_format.

Update existing tests and provide new ones to test new paradigm.