Feature/#165 move to center

[markusressel]

This adds a moveToCenter api method, as described in #165.

Btw, I have thought about your "recipes" idea, and - while I fully support this idea - I think, better than only writing a tutorial, is to write code in ZoomLayout, that actually implements these ideas, create a write-up of what the initial goal was, what the problems are and explain how the code works with a link to the actual ZoomLayout implementation (I mean the library here, not the class). That way the written code is always up to date, tested by actual ZoomLayout users, and migrated along the way as the library progresses. That way it can be used both as a functional API interface by users, as well as the code for a tutorial. Of course it has to be evaluated if a problem is worth including in the library, which is a fine.

[natario1]

Looks good!