[Feature] Simpler query for simple updates

[marcj]

For unit of work changes we apply a SQL CTE update technique to update very fast lots of changed entities. This is fast for lots of rows at the cost of complexity (which is fine since deepkit is designed for heavy workloads), but has an too big costs on very simple updates. Thus, we should add a simple UPDATE x SET y for small unit of work change sets (probably n < 2).