Extends NumberedPager to show a fixed rotated number of rendered pages

So far, NumberedPager was showing all existing pages. This pull request allows NumberedPager to limit the number of rendered pages by setting the field setMaxPages. If so, a fixed number of rotating pages is shown in the pager, i.e.

<< 1-2-**3**-4-5-6-7-8-9-10 >>

<< 5-6-7-8-9-10-11-**12**-13-14 >>

Also allows to customize the Next and Prev button labels.