Proposal for CODEOWNERS

GitHub has a feature called CODEOWNERS which will be especially beneficial in our mono-repo; https://help.github.com/articles/about-codeowners/

In particular we can assign codeowners to areas like `support` and `core`; when a change is made in one of those areas it will require a PR approval from one of the codeowners.

Here is an example CODEOWNERS file for the edgex-go repo (which can be placed directly in the root of the project.)

# These owners will be the default owners for everything in
# the repo. Unless a later match takes precedence,
# @edgexfoundry will be requested for
# review when someone opens a pull request.
*       @edgexfoundry

# In this example, @edgexfoundry/core-committers-team owns any file in a core directory
# anywhere in your repository.
core/ @edgexfoundry/core-committers-team

# In this example, @edgexfoundry/support-committers-team owns any file in an support directory
# anywhere in your repository.
support/ @edgexfoundry/support-committers-team

snap/ @edgexfoundry/snap-committers-team

# In this example, @doctocat owns any file in the `/docs`
# directory in the root of your repository.
/docs/ @edgexfoundry/docs-committers-team

It's worth noting that you can use individual GitHub handles and also restrict against files as well.