Update imports to use the new djblets.webapi modules.
Review Request #5900 — Created May 30, 2014 and submitted
In /r/5899/, djblets.webapi.core was split into different modules. This
updates the Review Board imports to use the new modules, instead of
relying on the legacy core module.
Unit tests pass.
This is a review from Review Bot. Tool: PEP8 Style Checker Processed Files: reviewboard/webapi/resources/draft_file_attachment.py reviewboard/webapi/resources/filediff.py reviewboard/webapi/encoder.py reviewboard/webapi/decorators.py reviewboard/webapi/resources/draft_screenshot.py Ignored Files: