SDK Refactor : match API structure

[ballinette]

• Update the SDK structure to match Kuzzle API.
• Use raw POJOs as input wherever objects structure is too complex or unpredictible

Fix all of following issues:
https://github.com/kuzzleio/kuzzle-backlog/issues/101
https://github.com/kuzzleio/kuzzle-backlog/issues/102
https://github.com/kuzzleio/kuzzle-backlog/issues/103
https://github.com/kuzzleio/kuzzle-backlog/issues/106
https://github.com/kuzzleio/kuzzle-backlog/issues/107
https://github.com/kuzzleio/kuzzle-backlog/issues/108
https://github.com/kuzzleio/kuzzle-backlog/issues/112
https://github.com/kuzzleio/kuzzle-backlog/issues/145

And also:
#278
#280 (=> webpack v4)

[codecov-io]

Codecov Report

Merging #290 into 6.x will increase coverage by 10.78%.
The diff coverage is 96.16%.

@@             Coverage Diff             @@
##              6.x     #290       +/-   ##
===========================================
+ Coverage   84.13%   94.92%   +10.78%     
===========================================
  Files          20       28        +8     
  Lines        1973     1319      -654     
===========================================
- Hits         1660     1252      -408     
+ Misses        313       67      -246

Impacted Files	Coverage Δ
src/networkWrapper/index.js	90% <ø> (ø)	⬆️
src/controllers/document.js	100% <100%> (ø)
src/controllers/realtime/room.js	100% <100%> (ø)
src/networkWrapper/protocols/abstract/realtime.js	96.96% <100%> (+44.58%)	⬆️
src/controllers/realtime/index.js	100% <100%> (ø)
src/controllers/searchResult/specifications.js	100% <100%> (ø)
src/networkWrapper/protocols/socketio.js	96.29% <100%> (+0.29%)	⬆️
src/Kuzzle.js	99.29% <100%> (+53.43%)	⬆️
src/controllers/bulk.js	100% <100%> (ø)
src/controllers/security/user.js	100% <100%> (ø)
... and 39 more

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