REACH-43 Zoom to fit in workspace

It is necessary to merge https://github.com/pboyer/flood/pull/20 before this one.

In this PR we added ability to zoom workspace elements to fit workspace area.
zoomToFit function executes next steps:
- get X and Y coordinates for all nodeViews;
- get minimum and maximum coordinates values;
- get center point of all nodeViews;
- calculate zoom rate;
- apply zoom on elements;
- calculate delta between workspace center and nodeViews elements center;
- apply that delta;