 Update BIP147 deployment times, nMinimumChainWork and defaultAssumeValid (#2030)
 Update BIP147 deployment times, nMinimumChainWork and defaultAssumeValid (#2030)

* Update BIP147 deployment times

* Update nMinimumChainWork and defaultAssumeValid of mainnet

biblepay/biblepay,dashpay/dash,thelazier/dash,ivansib/sibcoin,UdjinM6/dash,thelazier/dash,ionomy/ion,dashpay/dash,crowning-/dash,ionomy/ion,crowning-/dash,biblepay/biblepay,nmarley/dash,nmarley/dash,ivansib/sibcoin,thelazier/dash,nmarley/dash,crowning-/dash,biblepay/biblepay,biblepay/biblepay,UdjinM6/dash,crowning-/dash,UdjinM6/dash,dashpay/dash,ionomy/ion,UdjinM6/dash,ionomy/ion,dashpay/dash,dashpay/dash,thelazier/dash,biblepay/biblepay,crowning-/dash,UdjinM6/dash,biblepay/biblepay,nmarley/dash,ivansib/sibcoin,biblepay/biblepay,nmarley/dash,nmarley/dash,nmarley/dash,ionomy/ion,biblepay/biblepay,ionomy/ion,ivansib/sibcoin,ivansib/sibcoin,ivansib/sibcoin,thelazier/dash,crowning-/dash