#9 Add receive sensitivity information to interfaces

[Ian Lister]

In addition to the output information described by feature request
#998498 it would be nice if radio interfaces had receive sensitivity
information recorded. This would require multiple values per
interface (different signal levels for different data rates) and
should probably be based from a common table of radio devices
(perhaps with just a popup menu of known devices) - see
#998509.

In conjunction with #998498 and the existing free space loss
calculations this would allow automatic link budget calculations.

Ian