PX4 flight stack logging format support, slight cleanup of C code graphing functionality

Hi,

This is again 100% compatible with the existing logs / state and only adds support for PX4 logs plus slight cleanups of the C code plots (legends, consistent graph colors). If a GPSRawOut.txt file is present, it will be used to graph untouched raw GPS velocities (since VelN and VelE are not present in the existing fields).