kdenlive do not have icons in the toolbar while installed on non-KDE desktop

[Norbert]

Steps to reproduce:
1. Have Ubuntu MATE 19.10 installed
2. Install kdenvlive with `sudo apt install kdenlive`
3. Launch it with `kdenlive`

Expected results:
* kdenlive looks good, has icons on toolbar

Actual results:
* kdenlive looks weird, do not have icons on toolbar (see screenshot)

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: kdenlive 4:19.08.2-0ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-18.19-generic 5.3.1
Uname: Linux 5.3.0-18-generic x86_64
ApportVersion: 2.20.11-0ubuntu8
Architecture: amd64
CurrentDesktop: MATE
Date: Sat Oct 26 12:57:05 2019
InstallationDate: Installed on 2019-10-19 (7 days ago)
InstallationMedia: Ubuntu-MATE 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: kdenlive
UpgradeStatus: No upgrade log present (probably fresh install)