Allow to create group and its contest on UI

judge/widgets/__init__.py

@@ -2,3 +2,4 @@ from judge.widgets.checkbox import CheckboxSelectMultipleWithSelectAll
 from judge.widgets.mixins import CompressorWidgetMixin
 from judge.widgets.pagedown import *
 from judge.widgets.select2 import *
+from judge.widgets.datetime import *

judge/widgets/datetime.py

@@ -0,0 +1,24 @@
+from django import forms
+
+
+class DateTimePickerWidget(forms.DateTimeInput):
+    template_name = "widgets/datetimepicker.html"
+
+    def get_context(self, name, value, attrs):
+        datetimepicker_id = "datetimepicker_{name}".format(name=name)
+        if attrs is None:
+            attrs = dict()
+        attrs["data-target"] = "#{id}".format(id=datetimepicker_id)
+        attrs["class"] = "form-control datetimepicker-input"
+        context = super().get_context(name, value, attrs)
+        context["widget"]["datetimepicker_id"] = datetimepicker_id
+        return context
+
+    @property
+    def media(self):
+        css_url = "https://cdnjs.cloudflare.com/ajax/libs/jquery-datetimepicker/2.5.20/jquery.datetimepicker.min.css"
+        js_url = "https://cdnjs.cloudflare.com/ajax/libs/jquery-datetimepicker/2.5.20/jquery.datetimepicker.full.min.js"
+        return forms.Media(
+            js=[js_url],
+            css={"screen": [css_url]},
+        )

judge/widgets/select2.py

@@ -45,6 +45,7 @@ from django.conf import settings
 from django.core import signing
 from django.forms.models import ModelChoiceIterator
 from django.urls import reverse_lazy
+from django.utils.http import urlencode
 
 DEFAULT_SELECT2_JS = "//cdnjs.cloudflare.com/ajax/libs/select2/4.0.3/js/select2.min.js"
 DEFAULT_SELECT2_CSS = (