Move definition of next and previous arrows into translation file.

Previously the `&laquo;`, `&raquo;` and `...` were hard-coded into the paginator (when viewing a list of pages like:

```
<<  1  2  3  ...  6  7  8  >>
```

This PR takes those strings and looks for them in `app\lang\en\pagination.php` instead.  This allows you to redefine them (maybe using icons instead).

There will be a related PR on the laravel/laravel package as well, to add those strings to the default translation file.