Use babel-plugin-dedent in Review Board.
Review Request #151 — Created Nov. 15, 2016 and submitted
In another change, I've added an npm dependency to Djblets to install babel-plugin-dedent, which allows us to use ES6 template strings without filling our compiled output with a ton of ugly spaces. This change enables it for Review Board as well. Testing done: - Ran `setup.py develop` and saw babel-plugin-dedent get installed correctly. - Used the dedent tag in extension code. Reviewed at https://reviews.reviewboard.org/r/8515/