Add CHANGELOG.md with work from Sprint 12

@ManageIQ/core Please review

I'm taking a cue from http://keepachangelog.com and getting a change log into our repository based on the results from the [last sprint](https://github.com/ManageIQ/manageiq/issues?q=milestone%3A%22Sprint+12+-+Sept+9%2C+2014%22).  After the demo planning meeting this morning, I've taken the highlights from that, and put them into the change log as what was "Added".  However, there is still a little more to do before merging...

- Give a little more detail on the automate model changes (@gmcculloug @tinaafitz @mkanoor)
- Highlight the "major" bug fixes.

Any help you can give is appreciated.