This commit adds a sequence number to the IpnsEntry protobuf
that is used to determine which among a set of entries for the same key
is the 'most correct'.

GetValues has been added to the routing interface to retrieve a set of
records from the dht, for the caller to select from.

GetValue (singular) will call GetValues, select the 'best' record, and
then update that record to peers we received outdated records from.
This will help keep the dht consistent.

License: MIT
Signed-off-by: Jeromy <jeromyj@gmail.com>