Move them to the core/network packages, close#2950. The name of
mempool's unsorted transactions metrics has been changed along the
way to match the core's metrics naming convention.
Signed-off-by: Anna Shaleva <shaleva.ann@nspcc.ru>
Notes for witnesses:
* [N sig + M multisig + K contract] combination is possible where N, M, K >=0.
* Each verification script should be properly filled in.
* Each invocation script should either be empty or contain exactly one
signature.
