This adds support for the dependencies-v2 experimental flag when building a bundle.

* Add dependency v2 fields to the porter.yaml manifest
* Represent v2 deps in the bundle.json
* Determine which dependency extension is used by a bundle
* Have separate packages for the dependencies v2 cnab extension, and its implementation
* Updated porter schema command to output the experimental bundle schema when the dependencies-v2 flag is set

I have updated the mybuns test bundle with additional data so that it can be used in some of our unit tests (such as the cnab-adapter tests) so that we aren't maintaining a bunch of random test porter.yaml files that are all slightly different to hit all our required test cases. I'll follow up later and see if we can reuse it even more elsewhere.

While not an officially released version of the manifest, I have reserved 1.1.0 for bundles that define advanced dependencies. The schemaVersion of a bundle can only be set to 1.1.0 when the v2 dependencies experimental feature is enabled.

The docs still point to 1.0.1 as the latest version, and by default bundles are created with 1.0.1 and validated against 1.0.1. Once we are sure that our schema changes are solid and won't be modified further under the experimental flag (ideally waiting until the flag is removed) then we can release 1.1.0 and default to it.

Signed-off-by: Carolyn Van Slyck <me@carolynvanslyck.com>