Allow for widgets to restrict who can publish instances.

[FrenjaminBanklin]

Closes #1198.

Made a migration to track whether a widget is restricted for student creation or not.
Adjusted installer to account for a new install.yaml property corresponding to the new field.
Adjusted widget catalog lookup to omit author_only widgets when non-author users are looking at the catalog.
Fixed My Widgets page not properly disabling copy/delete buttons for users who lack appropriate access to a widget instance.

Essentially allows widgets to define themselves as 'non-student' widgets, meaning students cannot create new instances of them.

Release alongside ucfopen/Materia-Server-Client-Assets#47.

[FrenjaminBanklin]

Talked about it a bit, this might need to change.

Instead of restricting who can create a widget, adjust this idea - rather than only allowing basic_author users to create the widget, forbid anybody other than a basic_author from publishing the widget. Essentially non-authors can create and preview the widget, but in order to publish the widget it would need to be shared with somebody who has basic_author permission.

[clpetersonucf]

Reviewed:

• Added restrict_publish: Yes to a widget's install.yaml
• Created an instance of the widget as a student, received on-publish notification that the widget is restricted.
• Shared the widget with another user with the basic_author role
• basic_author user was able to edit and publish the widget
• Revoking the basic_author user and attempting to edit as the student user gave me a restricted access dialog

The process appears to work well. My only suggestion is that the on-publish notification doesn't suggest or provide any sort of action. Could we add a button to save the widget as a draft, or inform the user that they need to save the widget as a draft and share the widget with a basic_author user from the collab screen?

In the future, it'd be really cool if we could provide an option within that space to add a collaborator right then and there, instead of saving a draft and navigating to My Widgets first - but I think this is good for now.

[iturgeon]

Oh man, I like that inline collaborator workflow idea @clpetersonucf . Add it as a new feature issue