Demo.ipynb in the data-synthesizer module is not replicable

[havanagrawal]

Problem

1. Since the notebook adds/delete configurations, the first half of the notebook (Step 3) almost always errors out.
2. The code in step 4 refers to a specific file generated on a specific date. This will also error out if anyone runs the notebook as is.

Solution

1. Reorder the cells, so that the changes result in the original configuration of foregrounds.json and backgrounds.json being restored OR use a temporary config in the example.
2. Have the generate_synthetic_dataset return the paths to the train_image and train_mask directories.

[havanagrawal]

Fixed by #31