Change of data_XXX_txYYY.csv file columns' names

[pedropaulofb]

For improving the readability, please substitute the name of the column in the data_XXX_txYYY.csv file in the generation code as follows:

- Substitution 1:

• before: stereotype_original
• after: ontouml_stereotype

- Substitution 2:

• before: stereotype_gufo
• after: gufo_classification

Also, make the adjustments in the related variables names if necessary.

I have already made the modifications in the documentation.

[pedropaulofb]

@mozzherina, please solve this issue before the re-generation of the dataset.

[mozzherina]

Done