Project license should link to license

The appdata just says:
```
LicenseRef-proprietary AND GPL-2.0 AND LGPL-2.1-only
```

Ideally this would link to the license online, similarly to those other projects on Flathub:
```
LicenseRef-proprietary=https://botfather.io/docs/legal/tos/
LicenseRef-proprietary=https://code.visualstudio.com/license
LicenseRef-proprietary=https://raw.githubusercontent.com/snes9xgit/snes9x/master/docs/snes9x-license.txt AND LGPL-2.1
LicenseRef-proprietary=https://wwwimages2.adobe.com/content/dam/acom/en/legal/licenses-terms/pdf/Flash_Player_30_0.pdf
LicenseRef-proprietary=https://www.spotify.com/us/legal/end-user-agreement/
LicenseRef-proprietary=https://www.sublimetext.com/eula
```

Start by locating the appdata metadata containing the project_license entry and compare its format with the Flathub examples in the issue. Confirm the appropriate online license URL, then verify that the metadata retains the existing license identifiers while making the proprietary license link explicit.

Written by the indexing model from the issue text.