DO NOT MERGE: hardwired ux code for changing static pages to pages and allowing course nav manipulation
cleaning up the UI to match current story better
cleaning up the html and style for pages in Studio
Changed "Status Page" -> "Page".
Display list of "built-in tabs" on Pages page.
Added defensive code for tabs that do not have the 'name' field stored in the database.  This is short-term solution until the LMS and CMS code is refactored.
Changed CSS class from locked to fixed.
additional styling for fixed state on Studio Pages
add a new page action added to bottom of Studio Pages
restoring drag and drop on Studio Pages
initial check-in for tab refactoring.
Checkpoint for CMS-side changes.
checkpoint before introducing can_display method on tabs, which should make it easier to support LMS requirements.
checkpoint after studio working.
checkpoint after testing.