User should be able to set --size_of_nadir as percentage of image height in all modes

[himynamesdave]

User can enter whole numbers between 5 and 30.

--path_to_nadir must also be supplied.

[fqrious]

done

[himynamesdave]

@fqrious

When user does not set a size_of_nadir, the default value used should be 25 if path_to_nadir is passed.

No frame extraction, add a nadir with default size (25%) -- currently issue as nadir covers 100% of image

python3 gopro2gsv.py \
    --input_video tests/ski/GS016843.mp4 \
    --path_to_nadir stock_nadirs/without_gopro/trek_view_full_nadir.png \
    --output_filepath tests/output/mode1/test1/GS016843.mp4

No frame extraction, add a nadir with custom size (10%) -- works as expected

python3 gopro2gsv.py \
    --input_video tests/ski/GS016843.mp4 \
    --path_to_nadir stock_nadirs/without_gopro/trek_view_full_nadir.png \
    --size_of_nadir 10 \
    --output_filepath tests/output/mode1/test2/GS016843.mp4

[fqrious]

fixed