Refactor Deflation/ Reflation

[Brian Lewis]

Follows from issue #566.

Application code should be as insulated from the process of deflation/reflation as possible

To make the server's REST interface generic, it should only deflate data when requested by the client. This is triggered by

• the client passing a customer header "X-Json-Deflate"

• the api endpoint being marked up with the attribute [Deflatable]

[Brian Lewis]

task(dashboard): refactor reflateion of data in teacher dashboard

Resolves #586

→ <<cset e57660e616fc>>