test: Add tests for read_novatel_L1_data_files, and fix broken unittests

[madhavmk]

• Add tests for load_novatel() and load_novatel_std()
• Fix broken tests in test_loaders.py
• Add tests for spline_interpolate
• Remove jupyter notebooks Optimized_Kalman.ipynb and kalman_compare.ipynb
• test config.yaml modified to accomodate updated Configuration class
• Fully Addresses Issue #120 and Issue #226, and partially Addresses Issue #240

[madhavmk]

assert len(travel_data) == len(spline_interpolate)