During testing the state of Flatpak support in OpenSUSE, I've found a few
issues. This is one of them: GNOME Software allows me to add Flatpak
repositories and install any Flatpak application. At this point, I'd expect
that I can also launch and use the installed applications. However, that's not
possible because the required flatpak package is not installed.

Steps to reproduce:

1. Perform a clean installation of OpenSUSE Tumbleweed (2018-11-30 image) with
GNOME desktop.
2. Download Flathub repo file and install it with GNOME Software:
https://dl.flathub.org/repo/flathub.flatpakrepo
3. Refresh package database in GNOME software.
4. Search for and install any Flatpak application, e.g. Nostalgia.
5. Click the Launch button to launch the Flatpak application.
6. Search the app in Activities screen and launch it from there.

Expected result:

Re 5. The application is launched.

Re 6. The application is found in Activities screen and can be launched,

Actual result:

Re 5. The application is not launched nor any error is shown. No clue what's
wrong.

Re 6. The application is not found in Activities screen/list of applications.

The cause:

The application is not launched because the flatpak package is not installed.

Solution:

Add flatpak dependency to gnome-software package.