Gwenview failed to list file system listings (probably) when installed individually (without installing main kde desktop packages)

[林博仁(Buo-ren, Lin)]

## Bug Reproduction Steps ##
1. (Clean system without KDE software installed) Install `gwenview` package to install Gwenview
1. Launch Gwenview
1. Select Browse
1. Select any location that are available from the listing

## Expected Behavior ##
File system listings successfully listed without issue

## Current Behavior ##
* All listings are not shown, if you input '/' in address bar then press 'enter` the attached error dialog will appear: "URL cannot be listed<new line>file:///
* Following error message will be found:
couldn't create slave: "Unable to create io-slave:\nklauncher said: unknown protocol‘file’。\n"

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gwenview 4:15.12.3-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-36.55-generic 4.4.16
Uname: Linux 4.4.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Sep 9 08:29:55 2016
ProcEnviron:
 LANGUAGE=zh_TW:zh_HK:zh
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=zh_TW.UTF-8
 SHELL=/bin/bash
SourcePackage: gwenview
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.