* Update CHANGELOG with release notes URL.
* Update README with new release number & name.
* Update metadata.json with new tag & dependencies.
* Add release note prelude for Mitaka.
* Update Reno release note to drop prelude.
* Improve release note landing page.
Change-Id: I2af74f77e6fce6a6067c13e865b5bc2bd34f39f6