API: No way to retrieve events later than a certain point

[dragotin]

The current API only takes the parameters page number and number of entries to influence the subset of entries returned.

For a client that is not suitable. We need an API that provides all new entries that came after a certain point of time. That can either be done through ID or timestamp. The client needs a way to specify a number of events to be returned at a time (already there), but also a way to query how many new entries are new after a certain point.

This blocks https://github.com/owncloud/client/issues/3732, https://github.com/owncloud/client/issues/3728