eb0d34b Remove unused chainparam networkID (jtimon)

…cture

d1244f3 Fix UB in CChainParams unique_ptr subclasses destructor. (furszy)
cf20f43 Chainparams: Get rid of CChainParams& Params(std::string) (Jorge Timón)
eeea862 Chainparams: Use a regular factory for creating chainparams (Jorge Timón)
f9d585a More zerocoin unused functions and classes cleanup. (furszy)
029ce7b pivx-cli align -rpcport help message to init.cpp help message. (furszy)
3431977 Chainparams: Translations: DRY: options and error strings  Also remove SelectBaseParamsFromCommandLine and SelectParamsFromCommandLin (Jorge Timón)
ce7a792 Removed unused AreBaseParamsConfigured() (furszy)
508fec1 Chainparams: Replace CBaseChainParams::Network enum with string constants (furszy)
2a1f16c Chainparams: CTestNetParams and CRegTestParams extend directly from CChainParams (furszy)
0ed1a48 Refactor `Params().NetworkID() == CBaseChainParams::TESTNET` for IsTestnet() direct call. (furszy)

Pull request description:

  Made several updates to the base chain params structure and further cleanups over the zerocoin code:

  * Replaced `CBaseChainParams::Network` enum with string constants and unified better the network selection error + network help message (adaptation of dashpay#6235).
  * Removed unused NetworkID field from chain params (dashpay#5598).
  * Improved the network params creation using a proper factory (adaptation of bitcoin#8855).
  * Cleaned almost all the zerocoin related functions inside `zerocoin.h/cpp` and `zpivchain.h/cpp`.

ACKs for top commit:
  random-zebra:
    ACK d1244f3
  Fuzzbawls:
    ACK d1244f3

Tree-SHA512: c7ecb34045f9e14dc60130d3f7142c2f32c4c16f5678e871036db0b513ec3c416762a2464ff0d50383a50d345ea90f2c5958284657479c2becaaf9bf3936fcd3