Prepare steps in the query evaluation to avoid overhead of repeating work.

[JervenBolleman]

In pull request #GH-3354 I started working on this idea. In the query evaluation there is often work that needs to be done only once per query evaluation but currently is done over and over again. Adding a prepare step in the query evaluation would allow us to all that kind of work once per query evaluation. This can easily give a nice speed up for many queries.