CreateIdentityWizard: Fix "null" error message when length limit of URI / nickname is exceeded
- I've considered fixing fred to specify a message when creating the SizeLimitExceededException but the HTTPRequestImpl has no L10n member variable yet and dealing with size limits is UI stuff so placement in WOT makes sense.
- Use "length" instead of "size" in L10n because thats more userfriendly, but name the L10n key "Size" so people find it when searching for any existing L10n string for that exception.
- Also add German L10n since I'm a native speaker. From now on I shall always do that immediately. Sorry for not always having done it before.