Create script to help automate release process

[matt-boris]

Release process requires multiple updates to a version number, for example, in many different files.

A script that handled this change would be nice to have and the release notes would be able to be greatly minimized.

[leplatrem]

There could be a way to automate the publication of artifacts too:

https://github.com/mozilla-extensions/xpi-manifest/blob/master/manifests/template-example.yml.template#L36-L38