Quality control on connections

[tylerni7]

Some connections are junk: in particular, the L1C - L2C differences are constant, and the code-phase smoothing offset for the carrier-phase data is insanely high.

I tried to just drop all the data where C2C was not present but especially for older data, this removed lots of useful signals. We should probably do something smarter like simply remove connections where the carrier-phase ranging data is constant.