Add a failsafes config page

[1Blademaster]

Display and be able to configure the failsafe parameters for the drone.

[bensgilbert]

@1Blademaster what sort of interface were you envisioning for this?

https://ardupilot.org/plane/docs/apms-failsafe-function.html

[1Blademaster]

I'd like to be able to configure the battery failsafe params and general failsafe params (throttle failsafe, GCS, EKF, fence, etc). Doesn't need to go into individual bitmask params I don't think.