title: Fit given number of cells in uicollectionview per row
body: <p>I have a collection view and I would like to have let's say 4 cells per row. I know that to accomplish this all I need to do is divide <code>collectionview.frame.size.width</code> by 4. This is easy. However, what I can not figure out, is how to take into consideration the insets at the side of the collection view and the spacing between the cells. I have 10 pixel insets on the left and right of the collection view, as well as there is a 10 pixel spacing between the cells. How can I calculate the required cell width taking these 10 px insets into account?</p>