Add docstring for Importer.start_import()

Working toward #167
Minor Cleanup in controllers/importer.py

Thanks, pylint!
Improved Comments in models.settings.py
Fix Regression in Importer

In commit b635dd1c3971bb7c007a71f02e637d39bc2c5347, I changed the method
add_folders() into add_directories(), but I didn't update the
VisQtInterface class to go with it.
Starting to Comment controllers/analyzer.py

Working toward issue #167