Minor refactoring.
Implement Repository for interfaces and commands.
Split repositories into two files; add missing placeholder test files.
Remove DummyInterface.
Remove DummyCommand.
Change Interfaces to use new InterfaceRepository.
Change Commands to use new CommandRepository.
Add #find_by_name to allow finding resources by name.
Add #reset to empty the repository.
Remove since no longer required.
Add convenience/delegator method for repository.
Fix tests, update class interfaces.
Update README with half use case.
Add mechanism to activate/deactivate an interface;

This is used to determine if the interface is accepting input.
Whitespace and tidy up.
Improve repository querying.
Add more tests.
Update mechanism to activate/deactivate interfaces.
Remove default values.
Remove unnecessary self.