Started implementing site ownership verification. See #209.

I don't want to use dnspython because the library is really big.
Unless we do more complex query, I think by checking
``unique_code in response`` is good enough.

This commit includes a unit test to the new ownership module.
Add ownership check before we run the plugin. See #209 an see #212.
Add the code generation when site is checked to have site ownership verification.
Fixed #213. GET /sites?url=<site_url> now includes groups in the output.
Merge pull request #210 from yeukhon/issue#209

[in-progress] Started implementing site ownership verification. See #209.