Refactor Playable

[Dr-Blank]

this is a draft only, find discussion here

Description

• transfer attributes to playable class which are required by the methods it provides
• make it an abstract class
• playable is its own file to avoid circular import of media in to base

Fixes #1290

Checklist for affected classes

• Track
• Photo
• Playlist
• Movie
• Episode
• Clip

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have added tests when applicable

[JonnyWong16]

Playable should be further broken down in to AudioPlayable and VideoPlayable.

The lyric/subtitle methods are currently in Audio and Video but they only apply to Track and Movie/Episode.

Ref: #1303, #1305