Cleans up gitignore
Improves list command when no boxes are found
Removes obsolete code in boot scripts
Extracts to util prudentia dir
Refactors common behaviour for FactoryProvider:
 - add_box calls the create before adding the box
 - remove_box calls the destroy after removing the box
Adds Digital Ocean API library dependency to requirements
Adds new DigitalOceanProvider
Implements register and create provider functionality