set pager size #1356

I think we could pare this down a bit by moving most of this logic into `lib/MetaCPAN/Web/Role/Request.pm`

Something like:

```perl
sub get_page_size {
    my $page_size = shift->param('size');
    unless ( is_PositiveInt($page_size) && $page_size <= 500 ) {
        $page_size = 100;
    }
    return $page_size;
}
```

The controllers should consume this role by default, so this would cut down on some boilerplate.  If you're short on time, I can make these changes for you.  Just let me know.