Add 0-suffixed fields to GetIdentity.

The function is also used in GetIdentitiesByScore. Addresses bug #5729.
Fix missing Identity fields in GetIdentitiesByScore.
Fix missing Identity field in GetIdentity.

Also moves adding the Identity field into the field-adding function.
Merge branch 'issue-5729' of https://github.com/Thynix/plugin-WoT-staging into Thynix-issue-5729
Re-order parameters to have the standard order used in the whole codebase:
First the truster, then the trustee.
Notice that this stresses the "flow of trust" *from* the truster *to* the trustee.
Cache what is used twice, not what is used only once anyway.
Split up addIdentityFields into addIdentityFields, addTrustFields and addScoreFields:
- The old code did cause the call to addIdentityFields in handleGetIdentitiesByScore to re-query the Score object even though it was already known in handleGetIdentitiesByScore. This would have been a severe performance issue since handleGetIdentitiesByScore is heavy anyway.
Document why we duplicate the FCP reply - to provide a legacy interface
- Also, reorder the code to have the non-legacy stuff at first.