app and gizmo lifecycle management

[unional]

Dynamic install, disable/enable, reload app, etc is still far away.

But the deactivate design should be in place and implemented in preparing for that.

Two approaches:

export function deactivate() { ... }

// or

export function activate() { return () => { /* cleanup */ } }

UPDATE:

• deactivate: cleanup, will be handled by @unional/gizmo
• dynamic load: will be handled by @unional/gizmo
• dynamic install: likely not a concern to the core framework. Maybe a IDE/CLI utility
• disable/enable: hibernation, will be specific to just-web. Will be a breaking change, or maybe just a different gizmo.
• reload app: essentially hibernation should be sufficient.

[unional]

unional/async-fp#161