Split layout into multiple modules #525

Job	Run time
Clippy	1m 18s
Rustfmt	14s
Tests (macos-latest)	1m 20s
semver	52s
Build Wasm Examples (callback-example)	52s
Tests (ubuntu-latest)	1m 17s
Code Coverage	9s
Build Wasm Examples (basic)	52s
Tests (windows-latest)	1m 4s
Build Examples (3d_charts)	24s
Build Examples (images)	39s
Build Examples (maps)	27s
Build Examples (shapes)	35s
Build Examples (custom_controls)	25s
Build Examples (scientific_charts)	23s
Build Examples (kaleido)	1m 13s
Build Examples (subplots)	22s
Build Examples (ndarray)	28s
Build Examples (basic_charts)	25s
Build Examples (financial_charts)	28s
	13m 47s

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