Select current provider on EIP preferences.

- Don't disconnect logout signals, so when the wizard is triggered the
  UI can reflect the logout result.
- Restore the selected provider when 'other...' is selected *before* the
  provider_changed signal is emitted to avoid that option to keep
  selected in case of some error.
- Avoid the currentIndexChanged to be triggered when we load the providers.
You should explain why we need to block signals in here.