`jIO.util.stringify` was raising if the value of an object was undefined, this changes fix it and provides the same behaviour as the standard `JSON.stringify`

/reviewed-on !41

JSON.stringify is not stable by design and can not be used to generate the hash.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify

This commit adds a stable version of JSON.stringify, available at jIO.util.stringify.
Relying on the nearly same string representation will simplify compatibility.

Allow us to choose what to test because timeout tests and job management
tests take too much time.

Job queues are now saved in workspace at different moment

Job queues are now saved in workspace at different moment