core: added basic chain configuration

Added chain configuration options and write out during genesis database
insertion. If no "config" was found, nothing is written to the database.

Configurations are written on a per genesis base. This means
that any chain (which is identified by it's genesis hash) can have their
own chain settings.

core/vm/util_test.go

@@ -0,0 +1,9 @@
+package vm
+
+import "math/big"
+
+type ruleSet struct {
+	hs *big.Int
+}
+
+func (r ruleSet) IsHomestead(n *big.Int) bool { return n.Cmp(r.hs) >= 0 }