Selector.link_prev  -> Link to prev page, if any.
Selector.link_next  -> Link to next page, if any.

page_selector_cell  -> Loops over all page nums, setting these:
  Selector.Page.is_current -> True if page_num is current page.
  Selector.Page.page_num   -> Loop variable.
  Selector.Page.link       -> Link to page page_num.