DEV: implement model interfaces

[mgrady3]

This PR introduces the core data models to the new please package, starting by adding interfaces classes that later models will inherit from

Notable changes:

• Builds out further structure to the new please package, adding sub-packages for model, io, and ui code
• Adds traits as a project dependency - this package is used for static type validation for the core data models
• Adds abstract base classes for electron microscope images and electron microscope experiments that later models will implement

closes #6