Pagination to show only reasonable number of pages.

In the pagination mixin change `pages` to contain only the predefined amount of pages:
```
<< 1 2 3 *4* 5 ...  >>
<< ... *6*  7  8 9 10 ...  >>
<< ...  6  *7* 8 9 10 ...  >>
```
Add parameter:
- a new derived list of pages `pagesVisible`
- a config parameter `pagination-pages-visible-number`