Create and Delete Actions for non-multisites?

[kjbenk]

After some thought about the site endpoint I think that we should only be creating GET and POST/PUT actions since users will only be accessing or editing site options. I cannot see a use case where someone would create a new site option and I don't think it would be a good idea to allow users to delete one as well. Since the options are stored within the wp_options table I think having just having the ability to READ and UPDATE is the best choice.

For a multisite however I think we should allow for all four operations since a new table is created per site to store site specific data.

@danielbachhuber @rmccue thoughts?