fix(Markdown): render markdown in more secure way

This commit changes markdown sanitization behaviour in following way:

class, style and data-* attributes are removed by default. These attributes
open possible vulnerability vectors to attackers.

The original behavior of sanitizer (before this commit) can be enabled by *useUnsafeMarkdown* configuration option.
Use this configuration option with caution and only in cases when you know
what you're doing.

src/core/components/object-model.jsx

@@ -40,7 +40,7 @@ export default class ObjectModel extends Component {
     let requiredProperties = schema.get("required")
 
     const JumpToPath = getComponent("JumpToPath", true)
-    const Markdown = getComponent("Markdown")
+    const Markdown = getComponent("Markdown", true)
     const Model = getComponent("Model")
     const ModelCollapse = getComponent("ModelCollapse")