WIP: Adding new time options to the prefech time list of a store

What does this MR do?

Adding new time options to the prefech time list of a store.
Previous entries were off by 1 week.

How confident are you it won't break things if deployed?

Very.

Links to related issues

none

Slack discussion

https://yunity.slack.com/archives/C1T1ZM9A4/p1548859784030800

Checklist

• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))