removed debugger call.
added course_tab class when new tab is added.
fixed issue found by acceptance test - reordering newly added static tabs.
renamed css class "course_tab" to "course-tab".
changes per PR review:
  - remove analytics call
  - raise not implemented error for unsupported POST requests
Introduced new css class "sortable-tab" to prevent dragging tabs
into non-movable tabs.
Added acceptance tests for hiding wiki and reordering built-in-tabs.
Add acceptance tests for new reordering of pages feature.
Modified get_tab_by_slug API to be consistent with other get_tab_by_X APIs.
Added additional documentation.
Added additional wiki toggling acceptance tests.
Studio - revising markup, templates and styling for page editing UI:

* added in fixed state markup/logic
* added in collection markup/logic
* revised styling for page titles, collection, and fixed elements