Attendance API: pagination

Added pagination to the Attendance endpoint to make fetching larger sets of attendance data easier.

The total number of elements, the current page as well as the total number of all pages will now be available in the "metadata" block:

{
 "success":true
	 "metadata":{
		 "total_elements":2
		 "current_page":0
		 "total_pages":3
	}
 "offset":0
 "limit":200
 "data":[
	 0:{...}
	 1:{...}
	]
}