Feature/refactor resource descriptor structure

@mszenher Please review and merge.

This PR refactors the structure of the underlying YAML document to use hash keys vs. arrays of elements  with 'id' properties. Review this with a number of colleagues and the vote was 5:1 to convert to this structure. This effectively reverts the prior change to use arrays, but makes the encapsulation simpler.

All specs passing (pending spec and coverage will be addressed in next PR):

Finished in 3.26 seconds
208 examples, 0 failures, 1 pending
Coverage report generated (99.45%) covered.