Restore js_of_ocaml web interpreter #181

Job	Run time
Build Catala and generate CI Docker image	6m 52s
Run integrated tests	12m 41s
Build and test the language server	10m 41s
Build catala-examples and generate artifacts	10m 5s
Build Catala on Windows	0s
Publish static content to github-pages	0s
	40m 19s

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