Initialise services dependant on roles designation based on N+1
block so that Genesis roles extension work properly. There's not
much sence to fetch node roles information for the latest persisted
block because Designation contract itself makes designated nodes
responsible since the next subsequent block.
A part of #3228.
Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>
Everywhere including examples, external interop APIs, bindings generators
code and in other valuable places. A couple of `interface{}` usages are
intentionally left in the CHANGELOG.md, documentation and tests.
Which allows to enable/disable the service, change nodes, keys and other
settings. Unfortunately, atomic.Value doesn't allow Store(nil), so we have to
store a pointer there that can point to nil interface.
