Remove main folder name from sub-folder names in left pane

[j-ed]

Expected behavior

The mail app shouldn't show main folder names in front of each sub-folder name to improve the readability of the folder list.

Current behavior

The mail app always shows the main folder name in front of each sub-folder name. This wastes space which could be used to display the original sub-folder name.

Steps to reproduce

1. Open the Mail app.
2. Check open a folder with sub folders.
3. Check how sub-folders are being displayed.

Environment

Server Configuration

OS: Linux 4.9.218
Web server: Apache2 2.4.46
Database: MariaDB 10.2.24
PHP version: 7.4.8
Nextcloud version: 19.0.2
Nextcloud Mail app version: 1.4.1
IMAP mail daemon: Panda IMAP

Client Configuration

Browser: Mozilla Firefox 80.0.1
Operating system: Windows 10

[ChristophWurst]

This was just tackled with #3147 :)