New post type: snippets

[drodil]

Create a new post type called snippets that can be used to share code blocks. This requires a possibility to select language of the snippet and should automatically prefix content as ```language and suffix with ending marks. Rules:

• Language must be selected from dropdown list
• No code blocks inside the content
• No attachments
• No answers
• Comments are ok
• Rendering should be done in some good way in the UI