Wiring the Authoring GUI for allow image submissions

@wedaly @gradyward 
They should not be enabled by default. Authors should consider whether their assignment can be completed using raw text, as that is generally more compatible with a wide variety of tools that we might add in the future, or students might using on their end as alternative means of access (accessibility). 

A very large number of responses/submissions are going to be text based even without encouraging authors to use images. The most common case is just asking a student a question. Think about the kinds of answers you provided when you were taking classes in school. How often did you produce something that could only be explained with a picture?