between multiple link characteristics which are defined in the data file.
As a result, any type of link characteristic for the mote, wifi, or SDR
testbeds can be shown as long as it's in the file.  Also partial support
for metacharacteristics (things like the min/max/stddev of a single link's
primary characteristic).

Basically, a nice refactor into what I hope is complete flexibility
for display of any kind of link characteristic on any of our wireless
testbeds.