Merge branch 'stable-2.15'

* stable-2.15:
  bazlets: Replace native.git_repository with skylark rule
  Upgrade bazlets to latest stable-2.15 to build with 2.15.5 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.15 API
  Format all Bazel build files with buildifier
  Migrate (i.e. move) `tools/bazel.rc` to `.bazelrc`
  Update bazlets to build with current latest 2.14.14 API
  Make plugin compile against stable-2.15
  Add CSS styling to change message
  Allow change message to be inherited from parent project

Change-Id: I150a9e696c708db4a79f79594726ba41546b3704