Added DC battery PGNs to sample N2K data file

[thomasonw]

DC battery PGNs 127513, 127506, 127508

[tkurki]

As the original file is a real world capture file I would rather keep it as it is, with no crafted data.

I have been thinking about a separate repository for sharing data files independent of the server code. Comments?

[thomasonw]

I would offer, as this is THE N2K demo file it needs to contain examples for each and every type of message SignalK supports via the N2K provider. Should expand to include not only DC, but some AC ones, some engine data, tank values, temps, etc... Unlikely that will ever come from one boat. I like the idea of a data repository, perhaps place the origional pure file in there as an example of navigation file?

[tkurki]

Going with your additions.

And this is git, unless somebody takes drastic action the original is safe and sound in this repo.