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
For the tests its better to not use the timeout_commit, and to wait for all the
votes, because otherwise we can end up with timing dependencies in the testing
code which can lead to nondeterministic failures. That was part of the reason
for this change originally.