Rereleasing and redeploying without a build

[stuartpb]

Right now, plushu-config checks for build.iid before it plushooks release-app and deploy-app (plushu/plushu-config#1). However, plushu-domains doesn't check for release.iid before redeploying. I haven't checked, but I think that causes domains:add to fail when setting domains for an undeployed app.

I think these are the changes that need to happen:

• domains needs to check for an app's existence before doing each of its commands (as config does).
• release-env and start-web-deploy need to check for build.iid and release.iid, respectively, before taking action, since they may be called in a scenario where their prerequisite hasn't happened yet (the app has been created but not pushed and built).
• config should not check for build.iid before rereleasing, as the relevance of whether the release and deploy will happen is up to the release and deploy plugins. It's possible that another app lifecycle ecosystem could be implemented that uses different criteria for how release and deployment proceed (even performing release/deployment steps in the absence of a build).