Use more appropriate icons

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

## General infomration
It would be nice to have icons or images instead of just a netflix logo for every menu item that doesn't have a cover
### Prerequisites

* [x] Are you running the latest version?

### Description
In the current app, menu items are shown with a folder icon and a netflix logo on the side. I suggest that the netflix logos are replaced with different icons for each menu item. Also, it would be good if the genre items used the genre fanart pack used by the system instead of the netflix logo.
### Steps to Reproduce

1. [Open the app]
2. [Look at the menu icons]

## Context (Environment)
I'm using libreelec on a raspberry pi 2
### 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

[Descripe your environment a bit more detailed, are you using LibreElec f.e.]
I'm using a beta version of libreelec with Kodi 18 RC, using a raspberry pi 2 and a ps4 controller.

Thanks in advance!

Start by locating the menu rendering entry point and the assets used when an item has no cover. Compare the current Netflix logo fallback with the requested per-item icons and the system genre fanart pack. The work is done when menu items no longer use the Netflix logo as a generic fallback and genre entries use the requested artwork.

Written by the indexing model from the issue text.