Add actions to editor context menu and editor toolbar


![nb-markdown-plugin-editor-toobar](https://f.cloud.github.com/assets/738383/263334/011ce69a-8d68-11e2-9537-83715a2c9495.png)
I have added two actions(generate and view) to editor context menu and editor toolbar.
We can run these actions on editor soon.

Thanks.