This commit switches all usage of math/rand to cmn's rand. The only
exceptions are within the random file itself, the tools package, and the
crypto package. In tools you don't want it to lock between the go-routines.
The crypto package doesn't use it so the crypto package have no other
dependencies within tendermint/tendermint for easier portability.
Crypto/rand usage is unadjusted.
Closes#1343
save transactions to blockstore
move to a separate module
benchmark KVIndexer
batch write transactions
Benchmarks:
```
BenchmarkKVIndexerIndex-2 100000 516300 ns/op
PASS
ok github.com/tendermint/tendermint/blockchain/tx 56.506s
5,16 s for 10000 transactions
1 s for 2000 transactions
```
```
BenchmarkKVIndexerIndex-2 h 3000000 8622 ns/op
PASS
ok github.com/tendermint/tendermint/blockchain/tx 34.210s
86 ms for 10000 transactions
16 ms for 2000 transactions
```
```
BenchmarkKVIndexerIndex1-2 5000000 7160 ns/op
BenchmarkKVIndexerIndex500-2 20000 1750411 ns/op
BenchmarkKVIndexerIndex1000-2 10000 3573973 ns/op
BenchmarkKVIndexerIndex2000-2 5000 7836851 ns/op
BenchmarkKVIndexerIndex10000-2 1000 33438980 ns/op
PASS
ok github.com/tendermint/tendermint/blockchain/tx 209.482s
7,8 ms for 2000 transactions
```
[state] write test for ApplyBlock
review comments
- move txindexer to state
- fix type
save Tx Index as well
do not store tx itself in the result