Re-placing Image & Video Menu-options under File menu-option as Tabs


* View modified:
  - file.py: Two more dict variables passed, i.e. imageCollection & videoCollection that holds list of image & video document-objects respectively... similarly how files variable is passed!

* TemplateTag modified:
  - ndf_tags.py: In get_gapp_menubar() function, except Image & Video all other gapps are passed.

* Template modified:
  - file.html: List tags are added to show images and videos.. similarly how they are used to be listed under File Tab-section!