Move to Tools namespace

Since this repo exists as a meta-gem, purely for installing all the gems in one go, there is no need to follow the convention of having a `version.rb` that is required by `tools.rb` and then required by the gemspec - since there are no other files to be required or not it doesn't make a difference and could be hard-coded in `tools.rb` or even the gemspec.

However, I've decided to use the convention here as well because that makes it consistent with the other tools. Most of the people working on these tools will not be purely Ruby devs by trade, (e.g. may be web ops, developers in other languages, etc) so it's especially important to follow the principle of least surprise for people working on these tools.
Add gem_publisher and task to publish gem

This also adds the task to Jenkins, so when the version has changed, it will publish the new version to RubyGems. There are no tests to run and no code to build here - the only changes that will happen to this repo are changes to the version.
Add CHANGELOG and bump version

Also added release notes from a previous version. Previous versions were in the Vcloud namespace - since this hasn't been published previously though, this doesn't matter - following the same versioning for the sake of our users.
Merge pull request #188 from alphagov/publish

[#67235848] Publish gem