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.

TNL-46

I've changed Studio to catch JavaScript errors when rendering xblocks, log the error, but to then continue as normal. This means that the user is still able to interact with the xblock to delete, duplicate etc. This seems reasonable as the xblock is only rendered as a WYSIWYG representation so if it isn't fully interactive that shouldn't be a big problem.

STUD-2061

STUD-1856

Display "IS VISIBLE TO" when released and published

Reword staff lock prompt and notifications

Change "View Published Version" to "View Live Version"

Change "Unit Tree Location" to "Unit Location in Course"

Switch live content warning based on unpublished changes

Reword discard changes confirmation prompt

Reword unit location tip

Add "Edit the name" popup text for sections and subsections

Fix popup text for section and subsection titles

Add popup text for new section, subsection, and unit buttons

Reword popup for View Live button and add tests

Reword notification when removing staff lock

Update MessageView when has_changes changed

Change "Published" to "Published (not yet released)"

Change "Unpublished (Staff only)" to "Visible to Staff Only"

Fix bok_choy test by changing course separator.
Change format of the modal title to '[Subsection/Section Name] Settings'.
Improve bok_choy test stability.
Studio: correcting modal window size name for outline settings editor
Specify full date in bok_choy tests.
Refactor bok_choy tests.
Remove .modal-editor from basic-modal.underscore
Set classes in modal window dynamically.
Studio: revising outline edit modal tip content and overall size
Rename isEditable to isEditableOnCourseOutline.
Interpolate display name.
Use graded instead of format as flag.
Studio: revising outline settings edit modal size
Fix selectors in bok_choy tests.

Fix failing bokchoy tests

* correcting visual display of outline UI without content
* temporarily resolving page actions that should be hidden by default

* syncing up unit publishing state UI with stateful names/styles
* revising outline item status message display logic to show release status
* fixing publishState value typo in outline UI template
* refining and syncing incontext editor styling
* maintaining visual alignment of collapsed/expanded sections in outline UI
* simplifying page-level action styles on outline UI

STUD-1873

STUD-1726

Conflicts:
	cms/djangoapps/contentstore/views/item.py

STUD-1707

cleanup of unit, container, and xblock sass; added modules and layout sass; publishing states and actions on new unit

STUD-1707

STUD-1754