[GNSS/satorbit] Fix docstring formatting
[GNSS/receiver] Add vN, vE, and vD in the rx_class
Minor modifications on dataValid flags
[GNSS/receiver] Major modification on novatel.py. Change read_gps call.
1. read_gps will take rx_class instead of prn_class because TOW has been
moved up to rx_class (no longer in prn_class which is one level deeper)
2. Add docstring.
[GNSS/receiver] Add README for receiver class structure.
[GNSS/nav] code_phase_LS() and test file
1. Update code_phase_LS() input to rx_class instead of prn_class (need access
to TOW)
2. Add test for this function using NovaTel data set collected by
Adhika and Hamid