Read most protocol params from common/params.json

* Add params package with exported variables generated from
  github.com/ethereum/common/blob/master/params.json
* Use params package variables in applicable places
* Add check for minimum gas limit in validation of block's gas limit
* Remove common/params.json from go-ethereum to avoid
  outdated version of it

* GetCode
* GetNonce
* GetStorage
* GetBalance

The uncle rewards were changed in the block processor. This change will
reflect those changes in the miner as well.

ab81bf2 go fail

git-subtree-dir: tests/files
git-subtree-split: ab81bf28d6157657b0a1c0d598785f1ed23fdbb1

5f8a010 go fials
6f7924a add cppjit fail
c21f368 update genesis test
de7266b update js example test

git-subtree-dir: tests/files
git-subtree-split: 5f8a0103c0456f9467b402fde3db4bcde345d53b

Discovery bonding protocol

This a fix for an attack vector where the discovery protocol could be
used to amplify traffic in a DDOS attack. A malicious actor would send a
findnode request with the IP address and UDP port of the target as the
source address. The recipient of the findnode packet would then send a
neighbors packet (which is 16x the size of findnode) to the victim.

Our solution is to require a 'bond' with the sender of findnode. If no
bond exists, the findnode packet is not processed. A bond between nodes
α and β is created when α replies to a ping from β.

This (initial) version of the bonding implementation might still be
vulnerable against replay attacks during the expiration time window.
We will add stricter source address validation later.

The primary motivation for doing this right now is that old PoC 8
nodes and newer PoC 9 nodes keep discovering each other, causing
handshake failures.

Issue #613

Frontier/sec 29

- add validation on TxMsg checking for nil
- add test for nil transaction
- add test for zero value transaction (no extra validation needed)

- rename Validate -> ValidateFields not to confure consensus block validation
- add nil transaction and nil uncle header validation
- remove bigint field checks: rlp already decodes *big.Int to big.NewInt(0)
- add test for nil header, nil transaction

- add validate method to types.Block
- validate after Decode -> error
- add tests for NewBlockMsg

Frontier/513

Configurable CORS domain