Patch paged filter

[holtkamp]

When using the Filterable trait, one can choose to use filter() to get a first batch/page of results or filterAll() to get all results.

In some cases it is useful to be able to influence which page of the results to load.

For example, when filtering the SalesInvoices of a Contact and checking them for a specific CustomField (for example a UUID): when a lot of SalesInvoices exist for the Contact, you want to prevent using filterAll() which loads all SalesInvoices at once (which might exhaust the available memory), and go over the results in small batches. To do so, the pagination parameters per_page and page are needed.

Feel free to alter or squash commits...