Expose protocols classes

[Aschen]

What does this PR do?

Expose protocol classes (Websocket, Http and SocketIO) in the root module.
Also remove the networkWrapper.

Documentation PR: kuzzleio/documentation#180

How should this be manually tested?

Run this snippet and the unit tests:

const {
  Kuzzle,
  Websocket
} = require('./index');

const
  websocketProtocol = new Websocket({ host: 'localhost', port: 7512 }),
  kuzzle = new Kuzzle(websocketProtocol);

(async () => {
  try {
    await kuzzle.connect();

    console.log(await kuzzle.server.now());
  } catch (error) {
    console.log(error);
  } finally {
    kuzzle.disconnect();
  }
})()

Other changes

• Rename KuzzleAbstractNetwork to KuzzleAbstractProtocol
• Rename network occurrences by protocol

[codecov-io]

Codecov Report

Merging #341 into 6-dev will decrease coverage by 0.66%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##            6-dev     #341      +/-   ##
==========================================
- Coverage   97.23%   96.56%   -0.67%     
==========================================
  Files          28       27       -1     
  Lines        1410     1397      -13     
==========================================
- Hits         1371     1349      -22     
- Misses         39       48       +9

Impacted Files	Coverage Δ
src/protocols/websocket.js	98.07% <ø> (ø)
src/protocols/socketio.js	94.64% <ø> (ø)
src/Kuzzle.js	95.56% <100%> (-4.44%)	⬇️
src/protocols/http.js	92.77% <100%> (ø)
src/protocols/abstract/realtime.js	100% <100%> (ø)
src/controllers/realtime/room.js	100% <100%> (ø)	⬆️
src/protocols/abstract/common.js	91.89% <100%> (ø)

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[scottinet]

Great work 👍
A few minor remarks, but otherwise it looks good to me.

[ScreamZ]

Awesome good job @Aschen