Custom Search For TableScreen (take 2)

[jamonholmgren]

Check #639 for specifics. Pasting @sxross 's description here.

---

This enables TableScreen to be backward compatible if the user wants to use default search on title or search_text, but allows custom search to be specified. E.g.:

class MySearchable < PM::TableScreen
  searchable placeholder: "Search events", with: -> (cell, search_string) {
    return cell[:properties][:event_name].downcase.strip.include?(search_string.downcase.strip)
  }
end

For those wanting code that does not resist refactoring quite so much, you can specify a method:

class MySearchable < PM::TableScreen
  searchable placeholder: "Search events", with: :search_method

  # other stuff
  def search_method
    return cell[:properties][:event_name].downcase.strip.include?(search_string.downcase.strip)
  end
  }
end

Real world examples would probably be more complex.