Publish router descriptors rejected by the authorities or omitted from the consensus

Right now, if a relay is dropped from the consensus, or its descriptor is rejected outright by the directory authorities, we won't find out that it has happened unless someone notices that their relay isn't working and tells us, and we can't find out why it happened unless we read the directory authorities' log files.

The directory authorities should:

• archive all descriptors that are published to them, even if they are rejected or not included in the consensus;
• if a descriptor is rejected, record the reason in that archive; and
• if a relay is omitted from the consensus, record the reason in the archive.

The directory authority operators should:

• examine a sample of the descriptors that are not included in the consensus, for whatever reason;
• if the descriptors in the sample do not contain particularly sensitive information, begin publishing these otherwise unpublished descriptors.

Having this information available would make it easier to find relays that were disabled by #2204 (moved) and inform their operators that they need to upgrade Tor, for example.