Add the ability to reorder Pages and hide the Wiki page.
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
Support for "View Live" on Pages page.
Settings for ENABLE_STUDENT_NOTES and ENABLE_TEXTBOOK in CMS.
Do not display empty collection tabs.
Updated Changelog.
Merge pull request #3064 from edx/nimisha/studio-reorder-and-hide-tabs

Nimisha/studio reorder and hide tabs