Allow training of grass removal from multiple images.

[hargup]

We have a pretty clean code to generate and train the grass removal from image. The training data is saved in file Samples.model. When we run the sample generator again, the Samples.model file is replaced by a new file. Modify the code to append new training data to existing model file.

[hargup]

The issue is not valid. The sample generator already appends training data to new file.