add skip feature to feature_build.py

[openamiguel]

• [x] add command prompt option to rebuild/overwrite files in the features folder
  • if this option is not called, then skip all files already in the features folder
• [x] add if-statements to properly handle the following cases:
  • if rebuild and file in folder --> write to file
  • if rebuild and file not in folder --> write to file
  • if not rebuild and file in folder --> don't write to file
  • if not rebuild and file not in folder --> write to file

[openamiguel]

it turns out that this was unnecessary