chainreg: add Config, move chainparams.go

Creates a Config that initializes the chainregistry struct in the
lnd package. Also moves all of chainparams.go to the chainreg
package.

rpcserver.go

@@ -2584,7 +2584,7 @@ func (r *rpcServer) GetInfo(ctx context.Context,
 		BlockHeight:         uint32(bestHeight),
 		BlockHash:           bestHash.String(),
 		SyncedToChain:       isSynced,
-		Testnet:             isTestnet(&r.cfg.ActiveNetParams),
+		Testnet:             chainreg.IsTestnet(&r.cfg.ActiveNetParams),
 		Chains:              activeChains,
 		Uris:                uris,
 		Alias:               nodeAnn.Alias.String(),