Further optimize the write costs

[alexggh]

Even with the entire state fitting into the TrieCache writes will still have a cost of about ~10us per write, so we need to look into further optimizing this costs.

Some ideas of optimizations are:

• Run with a profiler and try to improve the trie calc algorithm.
• Disable writes to DB every block see Basti's suggestion here.
• Optimize writes to the DB by fine-tunne rocksdb.
• Use paritydb if that's better and ready for production.