Implement memory mode

[tonyc]

Read all the channels on startup.

for n = 0..119:
  Send MA0nnn;

• When receiving a MA0nnn command, parse it, and store the results somewhere.
• When receiving MA7fnnn...., read the frequency out of nnn
• When receiving a MNnnn command, display memory channel nnn as the VFO frequency.
• The undocumented MC nn command also indicates what memory channel has been changed to.

The radio doesn't seem to tell you what memory channel you're currently in when first switching from VFO to memory mode. See if there's a way to figure the currently active memory channel on startup.

[tonyc]

It turns out that mass-requesting the full memory channel details causes the radio to lock up in a weird way, so unfortunately I can't just download all the memory channels and then display e.g. the channel name.

I am going to just display the frequency/split info and the channel number, which will be good enough. ARCP doesn't display the channel name on the main display.

[tonyc]

This has been merged into develop