When object can't be found using current network map, there is a chance to find
it using netmap versions from previous epochs.
By default only current netmap is used. Well-known X-Headers can be used to set
the specific netmap version and limit how deep into the past the node can go in
the search of an object.
Signed-off-by: Stanislav Bogatyrev <stanislav@nspcc.ru>
This commit:
* moves Token message to service package;
* updates token structure (new verb field, some renaming);
* replaces VerificationHeader header with Token in object package;
* removes no longer used VerificationHeader message.
