Reapply "Replace chai and axios (#71)"

[chgeo]

This brings naxios etc back, reverting commit 45d153c.

Known failure patterns

• validateStatus can be falsy → fix: validateStatus can be falsy #73
• arraybuffer responses are not Buffers (see cds-graphql/test/tests/queries/variables.test.js, fixed here with 3a375d1 and there with chore: don't overwrite Axios headers graphql#223)
• axios.defaults.maxRedirects not supported, fixed with 6d60668, see cds-fiori/test/preview/routes.test.js
• Absolute URLs in requests failed, fixed with f3031cf
• containSubset too strict, fixed with d27e127, see cap/dev/test/capire/getting-started.test.js
• OData batch responses, see cds-mtxs/test/extensibility/ft-mt-custom-auth/ft-custom-auth.test.js → remove test
• Timeouts during debugging

Also:

• bring axios compat. back that kicks in if axios is installed

[chgeo]

@danjoa I had to revert the PR due to many test failures. Need to investigate the different error patterns, see above.