TNL-46
I've changed Studio to catch JavaScript errors when rendering xblocks, log the error, but to then continue as normal. This means that the user is still able to interact with the xblock to delete, duplicate etc. This seems reasonable as the xblock is only rendered as a WYSIWYG representation so if it isn't fully interactive that shouldn't be a big problem.
This commit implements STUD-1490, allowing creation of components
on the container page. It also enables the delete and duplicate
buttons now that new content can be created that would benefit.
Note that it also creates shared functionality for adding components,
and refactors the unit page to use it too.
