Add base-level support for extra_data to BaseResource.

Review Request #5205 — Created Jan. 7, 2014 and submitted — Latest diff uploaded

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Review Board
master

Reviewers

Add base-level support for extra_data to BaseResource.

Several of our API resources now support custom extra_data values. This
moves the support for this on the JavaScript side into BaseResource,
making it very easy for a subclass to work with extra_data.

All unit tests pass.

Tested manually with file attachments on image (which store coords in
extra_data), and with my new extensible fields support.