Fixes in calendar view and exam downloading

Ghost User
2019-08-13T13:07:29+02:00

Closes #898

This is already deployed in a hotfix on v25.

#### Previous behaviour
Steps to reproduce:

Check start time in list view of events, check exam download function and check events api with filter parameters

#### New behaviour
Steps to validate that it works:

Check start time in list view of events, check exam download function and check events api with filter parameters