Merge branch 'feature/registrations-starting-year-widget' into 'master'

Make starting year a dropdown in registration form

Closes #667

See merge request thalia/concrexit!869

(cherry picked from commit ccd627fe)

bd405422 Make starting year a dropdown in registration form

website/registrations/forms.py

 """The forms defined by the registrations package"""
 from django import forms
+from django.forms import TypedChoiceField
 from django.utils import timezone
 from django.utils.translation import ugettext_lazy as _
 
+from utils.snippets import datetime_to_lectureyear
 from .models import Registration, Renewal
 
 
@@ -20,6 +22,16 @@ class MemberRegistrationForm(forms.ModelForm):
         label=_('I accept the privacy policy')
     )
 
+    this_year = datetime_to_lectureyear(timezone.now())
+    years = reversed([(x, "{} - {}".format(x, x + 1)) for x in
+                      range(this_year - 20, this_year + 1)])
+
+    starting_year = TypedChoiceField(
+        choices=years,
+        coerce=int,
+        empty_value=this_year
+    )
+
     class Meta:
         model = Registration
         fields = '__all__'