Add JSON capabilities to navigator is not already present
Add JSON capabilities to navigator is not already present

When this lib is loading some ch specific functions are defined:
- ch.utils.JSON.parse
- ch.utils.JSON.stringify

These functions are only window.JSON extensions

Signed-off-by: Stéphane HULARD <a24f38cb8c57ec2778c80a9f0c151933508927e5@gmail.com>

CHStudio/ch.js,CHStudio/ch.js