Add a view specification to a trelliscope display

Usage

add_view(trdf, name, ...)

trdf: A trelliscope data frame created with as_trelliscope_df() or a data frame which will be cast as such.
name: The name of the view.
...: Any number of state specifications that define the view. These can be specified with any of state_layout(), state_labels(), state_sort(), filter_string(), filter_range().