Update db cache

Clean up shopping cart processor API.
Fix UUID JSON serialization bug in CyberSource2 implementation.
Update test suite to use new CyberSource2 implementation.
Fix i18n messages in CyberSource2
Enable CyberSource2 implementation by default.

It will now inherit from common settings.

disabling zendesk in lettuce tests and removing help/feedback lettuce tests in favor of the existing JS ones

Refactor get_parent_locations STUD-1663

Support incremental conversion of events from the old API to the new, in order to ensure the new system is working, enrollment events have been modified to make use of the new API.

All YouTube urls are defined on backend side.

Changed "Status Page" -> "Page".

UX:
    support for displaying built-in tabs
    restored drag and drop on Studio Pages
    additional styling for fixed state on Studio Pages
    add a new page action added to bottom of Studio Pages

Dev
    changes for viewing tabs in studio,
    refactored the tab code,
    decoupled the code from django layer.
    is_hideable flag on tabs
    get_discussion method is needed to continue to support
external_discussion links for now since used by 6.00x course.
    override the __eq__ operator to support comparing with
dict-type tabs.

Test
    moved test code to common,
    added acceptance test for built-in pages
    added additional unit tests for tabs.
    changed test_split_modulestore test to support serializing objects
that are fields in a Course.

Env:
    updated environment configuration settings so they are
    consistent for both cms and lms.

STUD-600

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

STUD-1206

[LMS-226]
[LMS-2013]

Refactored stub services for style and DRY

Added unit tests for stub implementations

Updated acceptance tests that depend on stubs.

Updated Studio acceptance tests to use YouTube stub server; fixed failing tests in devstack.

This reverts commit a517dc20.