- Ignore conflicting items which are uninstallable

- Ignore conflicting items which are uninstallable
- Create a "needed by" info if a requirement is still fulfilled.
- Allow only one needed_by and needed_by_capability in QueueItemInstall
- Added capability and type (REQUIRE, RECOMMEND,....) to
  ResolverInfoNeededBy
- Evaluate ResolverInfoNeededBy for more information in the error
  messages
- Enlarge detail description in the error messages