* Add new generic key_store interface
* Add new plaintext key store storing unprotected keys on disk
* Add new encrypted key store storing encrypted keys on disk
* Add new entropy mixing function using OS and go runtime sources

* Whisper protocol wasn't properly suppling envelope slices
* Message history wasn't properly propagated
* Added 'Messages' method, filtering any current envelope with the
  supplied filter.

JitVm struct stub. Forwards calls to DebugVm.

* proper 0xhex
* filters fixed
* start of filter manager
* accounts for ws. Closes #246

- the spec says response to getBlockHashes(from, max) should return all hashes starting from PARENT of from. This required major changes and results in much hackier code.
- Introduced a first round block request after peer introduces with current head, so that hashes can be linked to the head
- peerInfo records currentBlockHash, currentBlock, parentHash and headSection
- AddBlockHashes checks header section and creates the top node from the peerInfo of the best peer
- AddBlock checks peerInfo and updates the block there rather than in a node
- request further hashes once a section is created but then no more until the root block is found (so that we know when to stop asking)
- in processSection, when root node is checked and receives a block, we need to check if the section has a parent known to blockchain or blockPool
- when peers are switched, new peer launches a new requestHeadSection loop or activates its actual head section, i.e., the section for it currentBlockHash
- all tests pass

- AddBlockHashes ignores the first hash (just used to match getBlockHashes query) sends the rest as blocksMsg
- new test TestPeerWithKnownParentBlock
- new test TestChainConnectingWithParentHash
- adapt all other tests to the new scheme