Feature/joindin 397

This commit introduces a second SQL-Query that counts all matching
events. That total count is then added to the returned value and also
used to check whether there is a next page to be displayed or not
based on the requested LIMIT-parameters.

This changes the returned value in four ways:

* A new parameter ```meta.total``` is added to the returned values
* A new parameter ```meta.first_result``` contains the count of the first
  result being returned
* A new parameter ```meta.last_result``` contains the count of the last
  result being returned
* On certain occasions the next-link is not present where it was present
  before.

Aside of fixing issue #JOINDIN-397 with available "next"-link when no one is needed this PR also fixes an issue where a "previous"-link wasn't available when only one result has been returned. This issue has not yet been reported. 
This PR also now provides as a by-product all the required information to display something like 'Events 6-10 out of 325' as a result of the API-call.