chore(changelog): import changelog script from angular

`grunt bump` now generates `CHANGELOG.md` using this script. It reads the git
history and create section for fixes, features and breaking changes, including
links to closed issues and related commits.

It requires commit messages to be in the form described at:
https://docs.google.com/document/d/1JCFlkQ59Bx4qN1WKS1dtKXKl5G_lED6Lxey3iPNpQOs/pub
chore(changelog): add test and grunt task to run them
chore: update sublime config with test builds
chore: add git hook for validation commit messages
chore: add "init-dev-env" grunt task

To make it easier for people to initialize the development environment.
chore: update grunt tasks to produce valid commit msgs
chore(changelog): allow empty scope