use a sample of page number links for large collections

Large collections will have a large number of page links. The browser slows noticeably when inserting the large page links collection into the DOM.
add focus page number set around current page number
extract maxOptionSize to a pager widget configuration option
remove unused variable max_option_size
Merge pull request #711 from camallen/slow_page_number_links

Pager widget - slow table update when there are a large number of page number links