- Now user can select multiple drawables by holding "ctrl" key while selecting them.
- Enum type "EditionSubMode" has been renamed to "TransformationMode".
- Value TransformationMode::NONE has been added to previous enum.

- Fixed user interaction: transformation modes are no fixed anymore. Now user press 't', 'r' or 's' to enter in transformation mode, and he/she remains there until mouse button is pressed once more anywhere.