Adding "monitor" application to firmware
This app is used to measure receive level of given channels.
By pressing digits, the channel can be selected.
By pressing left or right button, the frequency is increased/decreased.
By pressing the menu button, the maximum received level is shown until
pressing menu button again. (usefull for hopping)
By pressing up or down button, the volume of a tone is changed, that
indicates rx level.
The left soft button is used to toggle PCS/DCS on shared channel numbers.
The right soft button is used to toggle uplink and downlink.