plugins: access permission control to plugins

[unional]

Each plugin will define what are the capability it needs,
and in turn, during activation it will receive a context with just those capabilities.

e.g.:

{
  "needs": {
    "errors": "read",
    "config": "write",
    "command": "write"
  }
}

export function activate(context: Context & ReadonlyErrorContext & ConfigContext & CommandContext) { ... }