Update RNodeInterface to add list of default setting parameters

[RFnexus]

This PR adds a list of default parameters for RNode devices that the user can select from. These parameters are the defaults for LoRa and RNode devices.

RNode options:

Bandwidth (in hertz):

7800
10400
15600
20800
31250
41700
62500
125000
250000
500000

Coding rate:

4:5 
4:6 
4:7
4:8

Spreading factor (7 - 12):

7, 8, 9, 10, 11, 12

TX Power (in dBm):

1 - 14

[liamcottle]

Hey! Thanks for this :)

I was planning to do something along these lines, but had left it til later...

It seems I didn't have permission to push commits to your branch with edits, so I've merged this in and made my changes directly in my main branch.

• Bandwidth labels are shown in KHz
• Reverted transmit power field back to using text input as the slider felt a bit annoying, and the limits wouldn't work in cases where someone makes hardware that allows for higher power levels.