Thumbnail/fanart confusion: use fanart as episode thumbnail in InfoWall

*I'm submitting a ...*
- [x] bug report
- [x] feature request
- [ ] support request

## General information

Maybe linked to #492?

### Prerequisites

* [x] Are you running the latest version? [v1.12.10]

### Description

When browsing TV shows, the fanart for the show and the thumbnail for the episode seem swapped.

This works fine in the list modes (though the background also uses the episode thumbnail, while I would expect the general fanart).


However, in the wall modes, the general fanart for the show is used for the thumbnails of all the episodes (but the episode thumbnail is still used as a background).


It seems to be working OK in the Information box: episode thumbnail overlaid over the show fanart (and episode thumbnail in the background).


Asking to “Show fanart” shows... what I would expect for the thumbnail.


If using “Choose art”, the only art available is the thumbnail, but as the “fanart”


### Steps to Reproduce

1. Go to a Season of a TV show (e.g., Octonauts, S4)
2. Flick through the display modes

**Expected behavior:**
1. The episode thumbnail is used in the description in List modes (this works)
2. The episode thumbnail is used as the icon of each episode in Wall modes
3. The episode thumbnail is used as the icone over the fanart in the informations (this works
4. (Maybe) The background doesn't change and uses the show's fanart

**Actual behavior:** [What actually happened]
1. Works as expected
2. The show fanart is used instead of the episode thumbnail
3. Works as expected
4. The episode thumbnail is showed as the background

## Context (Environment)

### Installation

* [ ] I installed the plugin via zip from the Releases page
* [x] I´m using the Netflix Repo
* [ ] I´m using a different source (Please tell which)

### Operating System

* [ ] Linux (x86/x64)
* [ ] OSX (x86/x64)
* [ ] Windows (x86/x64)
* [x] Linux (ARM)
* [ ] Android

#### Additional informatin on the environment

LibreElec Leia / Kodi 18.

Reproduce the issue by opening a TV show season such as Octonauts S4 and flicking through the display modes on Kodi 18. Compare the artwork used in list, wall, and information views; done means episode thumbnails appear on episode icons while the show's fanart remains the background where expected.

Written by the indexing model from the issue text.