Arm switch

This enables arming on a switch behavior.  To use this:

1. Assign an input channel to the Arming mapping
2. Set your arming settings to "Switch"

When the transmitter is connected and the switch is moved high, the system will arm.  If
the transmitter is disconnected the timeout will start running.  This can be disabled by 
setting "Disarm Timeout" to zero.

Note that the arming switch is still subjected to checking alarms, so if you have an alarm
it will not allow you to arm.

Fixes #608