Closes #12246: General cleanup of utilities modules

* Clean up base modules

* Clean up forms modules

* Clean up templatetags modules

* Replace custom simplify_decimal filter with floatformat

* Misc cleanup

* Merge ReturnURLForm into ConfirmationForm

* Clean up import statements for utilities.forms

* Fix field class references in docs

netbox/utilities/forms/widgets/datetime.py

@@ -0,0 +1,37 @@
+from django import forms
+
+__all__ = (
+    'DatePicker',
+    'DateTimePicker',
+    'TimePicker',
+)
+
+
+class DatePicker(forms.TextInput):
+    """
+    Date picker using Flatpickr.
+    """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.attrs['class'] = 'date-picker'
+        self.attrs['placeholder'] = 'YYYY-MM-DD'
+
+
+class DateTimePicker(forms.TextInput):
+    """
+    DateTime picker using Flatpickr.
+    """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.attrs['class'] = 'datetime-picker'
+        self.attrs['placeholder'] = 'YYYY-MM-DD hh:mm:ss'
+
+
+class TimePicker(forms.TextInput):
+    """
+    Time picker using Flatpickr.
+    """
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.attrs['class'] = 'time-picker'
+        self.attrs['placeholder'] = 'hh:mm:ss'