Refactor "mojito start" to be a wrapper around "node app.js"

The options `--port` and `--context` should now be handled by the bootstrap `app.js` file.

`mojito start` is now a simple wrapper to invoking `node app.js` for backward compatibility and the long term goal is to deprecate this sub command since users have total control over `app.js`.

The syntax `mojito start --port=9090 --context="environment:dev,device=iphone"` is still supported by having `app.js` extracting the arguments.

A template version of parsing the arguments can be added to the archetypes to `mojito-cli-create` package if required.

- [ ] Need to document that this only applies to Mojito#Next version (version tbd) and is not compatible with older Mojito version.
- [ ] Sync with `mojito-cli-create` so that archetype matches.
- [ ] Update `mojito-cli` package to have the correct `mojito-cli-start` version dependencies.