Login-button in navbar not always working

[gedankenstuecke]

While I was playing around with implementing #44 I noticed that the login button doesn't work on all pages, as the URL isn't passed to the template. Here's the pages affected by this:

• https://quantifiedflu.org/public-data/
• https://quantifiedflu.org/retrospective/event/{ID}
• https://quantifiedflu.org/report/public
• https://quantifiedflu.org/report/list/member/{ID}

[gedankenstuecke]

@madprime I've assigned you as this would be another low hanging fruit to fix before making another big push for getting people sign up 😄