Add fields for donations, bug tracker and translations

[Jacalz]

The field for homepage is there, but it would be great if we could input links for donations and bug tracker.

Example:

  <url type="bugtracker">https://github.com/Jacalz/rymdport/issues</url>
  <url type="donation">https://github.com/sponsors/Jacalz</url>

Also translations:

https://github.com/Beep6581/RawTherapee/blob/59a36d8f8a79918749a9da298bf559a0cedc4cf8/com.rawtherapee.RawTherapee.appdata.xml#L22

[darkdragon-001]

Maybe just allow adding all <url/> types. This could be done by having an additional type dropdown and adding a + button to add additional rows.

[ximion]

Patches are welcome ;-)

[darkdragon-001]

@ximion I proposed a patch in #52