conesnsu: follow up to removing some consensus params (#2427)

* follow up to removing some consensus params Refs #2382
* change args type to int64 in state#makeParams
* make valsCount and evidenceCount ints again
* MaxEvidenceBytesPerBlock: include magic number in godoc
* [spec] creating a proposal
* test state#TxFilter
* panic if MaxDataBytes is less than 0
* fixes after review
* use amino#UvarintSize to calculate overhead
0c74291f3b/encoder.go (L85-L90)
* avoid cyclic imports
* you can do better Go, come on
* remove testdouble package

state/tx_filter.go

@@ -0,0 +1,15 @@
+package state
+
+import (
+	"github.com/tendermint/tendermint/types"
+)
+
+// TxFilter returns a function to filter transactions. The function limits the
+// size of a transaction to the maximum block's data size.
+func TxFilter(state State) func(tx types.Tx) bool {
+	maxDataBytes := types.MaxDataBytesUnknownEvidence(
+		state.ConsensusParams.BlockSize.MaxBytes,
+		state.Validators.Size(),
+	)
+	return func(tx types.Tx) bool { return int64(len(tx)) <= maxDataBytes }
+}