Added abilitity to add custom CSS classes to field definitions.

doc/MANUAL.md

@@ -183,6 +183,9 @@ Structurally, they are made up of the following elements:
         - **`style`**: A string of inline CSS which will be applied to the field.
           **Optional**, **String**.
 
+        - **`classes`**: A string of optional CSS classes to add to this field.
+          **Optional**, **String**.
+
         - **`...`**: Other options, which depend on the type of field.  For
           more information, see [Field types](#field_types). **Optional**.
 

examples/customize/customize.json

@@ -12,7 +12,8 @@
                     "name": "background",
                     "title": "Different background color",
                     "type": "string",
-                    "style": "background-color: #C0FFC0;"
+                    "style": "background-color: #C0FFC0;",
+                    "classes": "foo bar"
                 }
             ]
         }

src/webapp.py

@@ -373,6 +373,8 @@ class ScriptFormWebApp(WebAppHandler):
             if field.get('required', None):
                 params['classes'].append('required')
 
+            params['classes'].extend(field.get('classes', '').split())
+
             params["style"] = field.get("style", "")
 
             # Get field-specific parameters