Add field type in template global variable
Add is_static_notebook field
Add is_notebook_static edition field (checkbox)
Generate correctly static URL (if static notebook)
ipythonExercice/ path isn't part of ipython_server_url anymore

It is now added by the XBlock, as sometimes we will add ipythonStaticNotebook
instead of ipythonExercice.
Merge branch 'add_is_static_field'