Removed usage of old is_active method in newsletters app

Closes #562

See merge request !681

Show cancellation dates in event admin

Closes #499

See merge request !659

Updated book list for the second semester

See merge request !677

Clean up registrations code smell

See merge request !675

Send website emails not from info@thalia.nu

See merge request !676

Send them from noreply@thalia.nu instead, as the site isn't allowed to send from info@

Testing this makes no sense, as it's a setting.

Fix wikilogin

See merge request !673

Remove python35-django11 testing on CI

See merge request !672

Use docker container from own namespace

See merge request !670

Fix event pages when user is not logged in

See merge request !666

Remove old prefetches from the mailinglists

See merge request !664

Really fix photos pagination this time

See merge request !663

Fix photos index view if more than 7 pages exist

See merge request !661

Add constraints to the members app

See merge request !658

Make partner optional for PartnerEvents

Closes #542

See merge request !653

Correct usage of django.utils.http.urlquote

See merge request !652

Enable booksale to freshmen before 01-09

Closes #474

See merge request !654

Filter the inline committee memberships

Closes #439

See merge request !655

Publicly show 'for members' menu-item

Closes #332

See merge request !656

Fix migration containing datetime

See merge request !657