Update stack-packet to be compatible with Crossplane v0.4.0

[hasheddan]

Crossplane [v0.4.0]() introduced a number of breaking changes including:

• Removal of portable resource classes [1]
• Moving all managed resources and resource classes to cluster-scoped [1]
• Introduction of claim scheduling controller and claim defaulting controllers [1]
• Introduction of forProvider / atProvider paradigm (not breaking) [2]
• Cross-resource references (not breaking, not applicable until reliant resources exist in this stack) [3]

The design of these components is reflected in the following docs: [1] https://github.com/crossplaneio/crossplane/blob/master/design/one-pager-simple-class-selection.md [2] https://github.com/crossplaneio/crossplane/blob/master/design/one-pager-managed-resource-api-design.md [3] https://github.com/crossplaneio/crossplane/blob/master/design/one-pager-cross-resource-referencing.md

stack-packet should be updated to be compatible with these changes.