[Discussion] Make the Server an external actor

[pragmaticivan]

Currently, we expose Server and ServerFactory on the project index.js (https://github.com/wedeploy/magnet/blob/master/src/index.js)

If the user decides to use a programmatically way by not using the CLI, it should allow the user to be able to set a server for the Magnet class.

• It should allow the user to create its own server configuration or even use another engine instead of Express.

const magnet = new Magnet({config, directory});

We currently don't accept a server on the constructor, maybe we can turn that into optional param:

const magnet = new Magnet({config, directory, server});

If a server is not provided, Magnet creates a server with express by default.

ps.: It could be solved by having a Get + Set for a Server, the set would be performed twice, so I would prefer having that into the constructor.

[eduardolundgren]

In order to achieve that we need to first make sure we don't rely on express proprietary apis, such as res.type() and so on, it's doable to rely only on Node interfaces to operate on response object. After that change we can expose the server as suggested.