Make Interactor::Schema::Context 1 for 1 compatible with OpenStructs

[berfarah]

There are a few methods from OpenStruct that have not been implemented.

This is not a super high priority for me, but I could see a case being made for this, since it'll help with drop-in compatibility.

Methods I'd consider implementing are:

• #delete_field
• #each_pair
• #eql?
• #modifiable as a reference to self