Musical Patterns - Pattern

Defines the structure of patterns: { id, material, metadata, spec }.

• id uniquely identifies each pattern.
• metadata has no "effect" per se. It's the blog post, formatted name, timestamps, etc.
• material is the code that makes the sounds: its properties and how they affect the output scales and voices and notes.
• spec is the controls for the material: configuration for how the user can adjust the properties (constraints, custom validation, etc), and presets.

A dedicated service exists for each of these properties.

Continuing in @musical-patterns/playroom and all pattern repos, to help organize thought, a common module structure matching this structure is used.