Restore js_of_ocaml web interpreter #172

Job	Run time
Build Catala and generate CI Docker image	1h 52m 18s
Build catala-examples and generate artifacts	10m 36s
Run integrated tests	12m 58s
Build and test the language server	8m 57s
Build Catala on Windows	0s
Publish static content to github-pages	-1s
	2h 24m 48s

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