Restructuring the project to make development easier;

- Move repository-backed models to subdirectory of repository;
- Move API#log to top-level for better access.
- Remove API#keypress (delegates to Keymaps#use).
- Remove API#event (delegates to Events#add).
Make model/repository more flexible;

- Move model and repository classes into methods.
Move colour related classes into colours/ directory.
Remove Positional;

Accepting the duplication for the time being.
Fix leaking #system_keys test.
Extract test classes to support;
Update development dependencies.