Fix restoring of OwnIdentities which had an edition inserted which cannot be parsed successfully:
- First of all move the code for determining whether a restore is in progress to a function. This can be used by the UI for telling the user about a pending restore.
- We should not insert a new edition while the OwnIdentity is in FetchState.ParsingFailed. Therefore, isRestoreInProgress returns true in that case and needsInsert() is changed to eat that return value and NOT  suggest inserting a new edition then. Previously, it would consider ParsingFailed as an OK state for inserting a new edition.
- Document the relation between OwnIdentity.isRestoreInProgress() and WebOfTrust.restoreOwnIdentity() in their JavaDoc