Split layout into multiple modules #523

Job	Run time
Clippy	1m 28s
Rustfmt	16s
Build Wasm Examples (basic)	51s
Code Coverage	12s
Build Wasm Examples (callback-example)	47s
Tests (windows-latest)	4m 35s
semver	52s
Build Examples (custom_controls)	32s
Build Examples (financial_charts)	30s
Tests (macos-latest)	2m 42s
Build Examples (ndarray)	24s
Build Examples (3d_charts)	24s
Build Examples (basic_charts)	25s
Build Examples (maps)	23s
Build Examples (shapes)	24s
Build Examples (images)	39s
Build Examples (kaleido)	1m 21s
Tests (ubuntu-latest)	2m 7s
Build Examples (scientific_charts)	31s
Build Examples (subplots)	25s
	19m 48s

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