Add edition support for shows

[JonnyWong16]

Description

• Add editionTitle attribute to the Show object.
• Add the EditionTitleMixin to Show to allow the editEditionTitle() method.
• The Season and Episode objects inherit the editionTitle attribute from the parent Show object (on the PMS side). The edition title for seasons and episodes is not editable.
• Refactor the editions() method into a mixin and add it to Movie, Show, Season, and Episode.

Ref.: https://forums.plex.tv/t/tv-show-editions-release/940424

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• 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