qt_gui_core: 0.2.26-0 in 'groovy/distribution.yaml' [bloom]

Increasing version of package(s) in repository `qt_gui_core` to `0.2.26-0`:

- upstream repository: https://github.com/ros-visualization/qt_gui_core.git
- release repository: https://github.com/ros-gbp/qt_gui_core-release.git
- distro file: `groovy/distribution.yaml`
- bloom version: `0.5.11`
- previous version for package: `0.2.22-0`

## qt_dotgraph

- No changes

## qt_gui

```
* prevent floating of plugins via double-click when -f flag is set (#48 <https://github.com/ros-visualization/qt_gui_core/issues/48>)
```

## qt_gui_app

- No changes

## qt_gui_cpp

- No changes

## qt_gui_py_common

- No changes