Constrain channel to valid values in the UI (#195)
Constrain channel to valid values in the UI (#195)

The valid channel list is conservative, but will be valid for all
regulatory domains, but ultimately we should retrieve the valid
channels from the API, so that we can include channels that are
valid for the current regulatory domain.

Opened #197 to capture work required to expose the complete
list of valid channels.
edwinsteele/biblebox-pi,edwinsteele/biblebox-pi,edwinsteele/biblebox-pi,edwinsteele/biblebox-pi,edwinsteele/biblebox-pi,edwinsteele/biblebox-pi