* Create new column family for local node info
* remove DBTransaction::new reliance on DB
* KeyValueDB trait
* InMemory KeyValueDB implementation
* journaldb generic over KVDB
* make most of `ethcore` generic over KVDB
* fix json tests compilation
* get all tests compiling
* implement local store (just for transactions)
* finish local store API, test
* put everything into place
* better test for skipping bad transactions
* fix warning
* update local store every 15 minutes
* remove superfluous `{}`s
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