libs/common: refactor libs/common 2 (#4231)

* libs/common: refactor libs/common 2

- move random function to there own pkg

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* change imports and usage throughout repo

* fix goimports

* add changelog entry

crypto/multisig/bitarray/compact_bit_array_test.go

@@ -7,12 +7,12 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
-	cmn "github.com/tendermint/tendermint/libs/common"
+	tmrand "github.com/tendermint/tendermint/libs/rand"
 )
 
 func randCompactBitArray(bits int) (*CompactBitArray, []byte) {
 	numBytes := (bits + 7) / 8
-	src := cmn.RandBytes((bits + 7) / 8)
+	src := tmrand.RandBytes((bits + 7) / 8)
 	bA := NewCompactBitArray(bits)
 
 	for i := 0; i < numBytes-1; i++ {