Newsletter is not responsive
### One-sentence description
When opening the Thalia newsletter via email on a narrow screen, the email clips at the right side.
### Current behaviour
See capture below. While a scrollbar is being displayed at the bottom of the mail, you can't expect readers to scroll down and up again to read both parts of each sentence.

### Expected behaviour
The width of the email scales with the width of the container in a responsive way.
### Steps to reproduce
1. Open the Thalia newsletter in a mail client, or open the online version in a browser.
2. Narrow the screen down. The scrollbar should appear at 744 pixels. Readability issues start at ~720 pixels.
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Als je de view breder maakt, blijft de container mooi gecentreerd, maar als je view wat kleiner is, moet je horizontaal scrollen, wat flink irritant is.
De 'most-outer' container past zich wel aan, maar deze blijkt geen effect te hebben op de content-container.
issue