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/bench_test.go

@@ -168,7 +168,7 @@ func benchInsertChain(b *testing.B, disk bool, gen func(int, *BlockGen)) {
 	// Time the insertion of the new chain.
 	// State and blocks are stored in the same DB.
 	evmux := new(event.TypeMux)
-	chainman, _ := NewBlockChain(db, FakePow{}, evmux)
+	chainman, _ := NewBlockChain(db, &ChainConfig{HomesteadBlock: new(big.Int)}, FakePow{}, evmux)
 	defer chainman.Stop()
 	b.ReportAllocs()
 	b.ResetTimer()