Shared - Refactor timelines

[Joery-M]

Timeline definition

This issue explains what 'timelines' represent in the application.

A timeline is a collection of Timeline items (#257) that, when rendered with Daguerreo (#33), can output an image.

Timelines manage inserting, removing, moving and other general tasks including Timeline items.
Timelines also manage playback.

When creating a timeline, some basic options need to be defined:

export interface TimelineSettings {
	name: string;
	width: number;
	height: number;
	fps: number;
}

Storage

A timeline inherits from Media (#245) using the following properties to extend the base metadata:

• Width: number
• Height: number
• FPS: number
• Timeline items: An array of ID's referencing Timeline items (Shared - Refactor Timeline Items #257)