* remove blocking sync -> import-queue operations
add specialization to testnet
remove add peer default impl on TestNetFactory
* remove empty brackets from dummy specialization
* nits
* make mut_peers take an fn once
* add SpecializationFactory trait in test
* remove add_peer imple in grandpa, fix typo
* use cmp::max for best importing number comparison
* remove import of non-existent create_peer
* add sender to start message