Fix some small bugs in the automatic newsletter event code

Ghost User
2019-04-17T19:35:40+02:00

Closes #861

#### Previous behaviour
Steps to reproduce:

1. Create a newsletter event and automatic dropdown
2. Entered end date does not match the end date of the event
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1. The costs are never shown in the newsletter preview...

Closes #861 (closed)

Previous behaviour

Steps to reproduce:

1. Create a newsletter event and automatic dropdown

2. Entered end date does not match the end date of the event

1. The costs are never shown in the newsletter preview

1. The automatic event selection always uses the dutch event title in the dropdown

New behaviour

Steps to validate that it works:

1. Create a newsletter event and automatic dropdown

2. Entered end date matches the end date of the event

1. The costs are shown in the newsletter preview when price > 0 and the checkbox is checked

1. The automatic event selection uses the current language title in the dropdown