Change event reducer to reset events to initial state on FETCHING action

Ghost User
2018-01-24T20:47:57+01:00

1. Open the app on iOS
2. Open event 1
3. See the information of event 1
4. Open event 2
5. See the information of event 1 and a loading indicator
6. See the information of event 2

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

1. Open the app on iOS
2. Open event 1
3. See the information of event 1
4. Open event 2
5. See a loading indicator
6. See the information of event 2