JSON support: string '/' encoding

`JSONValue.escape()` causes also slashes to get protected by backslashes, which I don't consider as being correct.

https://github.com/jolie/jolie/blob/a641b18b3d5f03a31674f5059aacc24dc2c39f97/lib/jolie-js/src/main/java/jolie/js/JsUtils.java#L65

E.g.
`
API listens under /api/user/...
`
gets converted into
`
"API listens under \/api\/user\/..."
`

What do you think?