Fix Device DNA and other Piksi hardware bringup functionality

Pull request #44 fixed a few issues with Piksi hardware bringup, but was never merged, so this closes #44 and provides that functionality on top of the latest master.

Fixes:
Being able to read Device DNA and program the encrypted DNA to the FPGA configuration flash.
Piksi sends acquisition result messages / Python class now exists to receive them.


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Maybe move this into its own function in init.c such that it can be called easily from the tests as well?