add namespace for app commands
add namespace for dyno commands
add namespace for env commands
standardize main usage formatting
Parse app flag globally but from command options

Instead of `hk -a myapp cmdname`, this reverts back to the
`hk cmdname -a myapp` syntax. However, parsing the `-a app` param is
still handled by the main executable rather than the subcommands or
plugins.
let commands say they need the app param
add namespaces for release and addon