Rewrite of the Node API

Description

The Node API used to be hard to use, not very understandable and quite inefficient.

This MR rewrites it entirely and makes aprt of it public so developers can directly use it in plugins.

Changes proposed in this merge request:

• Rewrite the Node API
• Make part of the Node API public
• Remove accessors to the Node API from Plugin

Benchmarks

Those benchmarks are run against the latest master as an indication of what will the change be when merged

First one was run 6 times, dropping the first of each, on base-files.bst

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commit	action	python_version	max_memory	time
bschubert/node-api-split - 55931ca9	build - 12	py37	190	94.44
	build - 4	py37	190	104.56
	build - 8	py37	190	96.29
	show	py37	191	4.75
	show - cached	py37	191	4.82
master - 199f080f	build - 12	py37	184	94.36
	build - 4	py37	184	104.39
	build - 8	py37	184	95.4
	show	py37	162	5.43
	show - cached	py37	185	5.28

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Second one was run 12 times, dropping the first two of each, on debian-stack.bst

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commit	action	python_version	max_memory	time
bschubert/node-api-split - 55931ca9	show	py37	1616	66.42
master - 199f080f	show	py37	1550	70.79

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