cmd/evm, core/vm, test: refactored VM and core

* Moved `vm.Transfer` to `core` package and changed execution to call
`env.Transfer` instead of `core.Transfer` directly.
* core/vm: byte code VM moved to jump table instead of switch
* Moved `vm.Transfer` to `core` package and changed execution to call
  `env.Transfer` instead of `core.Transfer` directly.
* Byte code VM now shares the same code as the JITVM
* Renamed Context to Contract
* Changed initialiser of state transition & unexported methods
* Removed the Execution object and refactor `Call`, `CallCode` &
  `Create` in to their own functions instead of being methods.
* Removed the hard dep on the state for the VM. The VM now
  depends on a Database interface returned by the environment. In the
  process the core now depends less on the statedb by usage of the env
* Moved `Log` from package `core/state` to package `core/vm`.

core/vm/vm_jit.go

@@ -30,6 +30,7 @@ void  evmjit_destroy(void* _jit);
 */
 import "C"
 
+/*
 import (
 	"bytes"
 	"errors"
@@ -385,4 +386,4 @@ func env_extcode(_vm unsafe.Pointer, _addr unsafe.Pointer, o_size *uint64) *byte
 	code := vm.Env().State().GetCode(addr)
 	*o_size = uint64(len(code))
 	return getDataPtr(code)
-}
+}*/