isSidebarFitsViewport ignores top spacing!

As the title says, the isSidebarFitsViewport function doesn't take into consideration the top spacing.

I've updated the function to be like this:

`isSidebarFitsViewport(){
    return this.dimensions.sidebarHeight + this.dimensions.topSpacing < this.dimensions.viewportHeight;
}`

It might want to take into consideration bottom spacing though as well.