Kovan WASM fork code (#7849)

* kovan fork code

* introduce ethcore level vm_factory and let it fail

* fix json tests

* wasmcosts as option

* review changes

* wasm costs in parser

* fix evm tests

* review fixes

* fix test

* remove redundant json field

ethcore/light/src/lib.rs

@@ -60,7 +60,6 @@ extern crate ethcore_bytes as bytes;
 extern crate ethcore_transaction as transaction;
 extern crate ethereum_types;
 extern crate ethcore;
-extern crate evm;
 extern crate hashdb;
 extern crate heapsize;
 extern crate futures;