Hue should support connecting to Livy when CSRF protection is enabled in Livy

Livy supports a configuration parameter in the Livy conf:

livy.server.csrf-protection.enabled

...which is false by default.  But if a Livy admin wants to enable it, Hue cannot support it.  Upon trying to launch a Livy session from the notebook, Hue will pass along the connection error from Livy as a 400 response that the "Missing Required Header for CSRF protection"

This work should enable Hue to pass the CSRF custom header and also provide for the Hue ini conf to switch this functionality on or off from a conf parameter.{{}}