LowPowerLab
Add new USB command to reset settings to defaults, clean up compiler warnings
Adds a new USB interface command ! that resets all runtime settings to default variables. Does not change the calibration values.
This makes automation much easier because can easily put the CurrentRanger into a known state. This makes it possible to, say, blindly send the string "!a34fu" and the CurrentRanger will reliably start streaming nanoamp values in the nanoamp format with BIAS disabled and LPF enabled. I do not think there is a way to do ths robustly with the previous firmware.
Also fixes up the three trivial compiler warnings by adding some parenthesis and adding a typecast.
Note that I have only updated the source code file and not the firmware image in this PR. Since these images are artifacts, I'd recommend moving them out of the repo entirely, and instead putting them into releases. LMK if you want more info on why this is the prefered approach or how to do it.
I don't see compiler warnings, so not sure what that one is about. I could merge the ! command changes but not everything else in this pull.
