Utilize annotations to compute spread requirements

[brooksmtownsend]

While implementing #75, I realized that we aren't using annotations to mark actors that are managed by wadm. In addition to being managed by wadm, we'll also want to note the specific Spread that the annotation is using so that we can manage conflicting actor spreads.

Until this is complete, the ActorSpreadScaler as implemented in #75 will not be able to properly handle multiple spreads that match to the same host and it's recommended to keep spread requirements as specific as possible.

[brooksmtownsend]

That's what I get for missing a review, looks like #76 adds annotation support. Will retrofit #75 to work with these changes