Add Steven Danna as a maintainer of Dev Tools

I've fixed a number of chef-shell and knife related bugs, written a
number of popular knife plugins that build on top of these systems,
and understand the related code well.
Merge pull request #2485 from opscode/ssd/maintainer-app

Add Steven Danna as a maintainer of Dev Tools
Adding myself to relevant component maintainer
Merge pull request #2490 from jtimberman/jtimberman/maintainers

Adding myself to relevant component maintainer