Use __file__ for paths instead of sys.path

[jbitton]

Using sys.path to determine the paths in base_paths.py is hacky and only works if your Python path is set very specifically.

Instead let's get the file paths in base_paths.py by using __file__ and getting the parent directories' names :)

Ran transforms test for each modality to ensure everything runs as expected:

$ ~/anaconda3/envs/augly/bin/python -m unittest augly.tests.text_tests.transforms_unit_tests
----------------------------------------------------------------------
Ran 12 tests in 0.013s

OK

$ ~/anaconda3/envs/augly/bin/python -m unittest augly.tests.image_tests.transforms_unit_tests
----------------------------------------------------------------------
Ran 39 tests in 14.366s

OK

$ ~/anaconda3/envs/augly/bin/python -m unittest augly.tests.audio_tests.transforms_unit_tests
----------------------------------------------------------------------
Ran 24 tests in 7.878s

OK

$ ~/anaconda3/envs/augly/bin/python -m unittest augly.tests.video_tests.transforms.composite_tests

----------------------------------------------------------------------
Ran 11 tests in 29.982s

OK