Update changelog handling, (1/2):

- Remove changelog handling from UpdateInfo class
- Change from an per update related changelog to a general changelog
- Allways fetch the changelog to show the newest changelog
- Remove displaying the changelog by clicking on the available updates
- Add a changelog preference:
  - Open changelog depending on the selected update channel, (release- and beta channel)
  - Open a dialog to choose the release- or beta changelog to show (all channel)
- Add a possibility to overwright the changelog uri by a system property (dk.changelog.uri)
- If the system language is set to german, show a german version of the changelog,
  otherwise show the english version