Proposal: Modular components and cleaner environments

In summary:
* Introduce the concept of _targets_, easily allowing an environment to
  target specific components.
* Add optional hierarchy structure to components, for grouping and
  reusability.
* Allow environments to operate on multiple _destinations_.
* Consolidate shared environment metadata and configuration files.

Signed-off-by: Jessica Yuen <im.jessicayuen@gmail.com>