LogInPage: Use API for CreateOwnIdentityWizardPage construction instead of doing it manually.
Add Identity.getShortestUniqueNickname():
- Don't actually implement it yet as this is quite a bit of work.
- We add it now nevertheless so we can use it in the web interface.
LogInPage: Use Identity.getShortesUniqueNickname() instead of duplicating its code.
- Notice that getShortestUniqueNickname is not actually implemented to compute a short nickname yet, but there is a bugtracker entry for it. So we can remove the TODO