Support for more types of cells

Supports slider and text field type cells. Also supports grouping of cells
I see what you're going for here, but this will evaluate to true for every single entry that's not a group, so you're allocating a mutable array over and over and over again.

I think if the very first item isn't a group, then create an empty section to start putting items in. As soon as we hit a group, there will be a new section as `currentSection`. If we *never* hit a group, there's only one section with an empty title.