Closes #11294: Markdown Preview (#11894)

* MarkdownWidget

* Change border and color of active markdown tab

* Fix template name typo

* Add render markdown endpoint

* Static assets for markdown widget

* widget style fix and unique ids based on name

* Replace SmallTextArea with SmallMarkdownWidget

* Clear innerHTML before swapping

* render markdown directly in template

* change render markdown view path

* remove small markdown widget

* Simplify rendering logic

* Use a form to clean input Markdown data

---------

Co-authored-by: Jeremy Stretch <jstretch@ns1.com>

netbox/extras/forms/misc.py

@@ -0,0 +1,14 @@
+from django import forms
+
+__all__ = (
+    'RenderMarkdownForm',
+)
+
+
+class RenderMarkdownForm(forms.Form):
+    """
+    Provides basic validation for markup to be rendered.
+    """
+    text = forms.CharField(
+        required=False
+    )