Move more params to the common section. (#6134)

* move common forks and parameters to common params

* port specs over to new format

* fix RPC tests

ethcore/src/snapshot/tests/test_validator_contract.json

@@ -3,7 +3,6 @@
 	"engine": {
 		"authorityRound": {
 			"params": {
-				"gasLimitBoundDivisor": "0x0400",
 				"stepDuration": 1,
 				"startStep": 0,
 				"validators": {
@@ -17,6 +16,7 @@
 		}
 	},
 	"params": {
+		"gasLimitBoundDivisor": "0x0400",
 		"accountStartNonce": "0x0",
 		"maximumExtraDataSize": "0x20",
 		"minGasLimit": "0x1388",