Markdownify the 'notes' field for StockItem

- New tab interface for the StockItem page
- Display / editing of notes field with markdown

InvenTree/stock/migrations/0018_auto_20200202_0103.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2.9 on 2020-02-02 01:03
+
+from django.db import migrations
+import markdownx.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0017_auto_20191118_2311'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stockitem',
+            name='notes',
+            field=markdownx.models.MarkdownxField(blank=True, help_text='Stock Item Notes'),
+        ),
+    ]