Rename stacks resources stackServices, serviceComponents and operatingSystems

Existing names are not consistent with the remaining api which uses an '_' instead of camel case.
Also these names are unnecessarily long. Since these names are not under the cluster resource, it is ok to reuse the names service and component for a more concise url.
So, the new stack api hierarchy would be:
stacks/versions/services/components/...
stacks/versions/operating_systems/...

Note This will not affect the stacks2 api that the UI uses.