article lock/unlock feature

[mydearxym]

when a article-like content in follow situations:

• the problem mentioned in article is solved
• has published very long time, the content has no value
• has no point, but not to the delete level
• etc

we should set a 🔒 flag on the content, and no edit or comments will be made/append

a possible prototype may look like this:

field(:lock, :string)
belongs_to(:lock_operator, User)

and if front-end want the lock history, should check the inner-logger, see: #104