Make sure all Web API definitions and docs list when things were added.

This change audits the webapi definitions to make sure that every field has an
'added_in' annotation. It also audits the webapi docs to have a 'versionadded'
field for each resource that was added post-1.5.

Testing Done:
Used git blame, git log, and git tag to find the commit that added each field.
Built the docs.

Reviewed at https://reviews.reviewboard.org/r/6680/