Remove bootstrap-datepicker-plus dependency, use native HTML selectors

apps/registration/forms.py

@@ -99,6 +99,10 @@ class StudentRegistrationForm(forms.ModelForm):
     """
     A student can update its class, its school and if it allows Animath to contact him/her later.
     """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields["birth_date"].widget = forms.DateInput(attrs={'type': 'date'}, format='%Y-%m-%d')
+
     class Meta:
         model = StudentRegistration
         fields = ('team', 'student_class', 'birth_date', 'gender', 'address', 'zip_code', 'city', 'phone_number',