Sophisticate-ify domain checking, integrate into security module

* Should also add in URL reversal to utils/urls.py
* Have it respect the security thing in use

```
security.py
51 async def check(typestring, querydata):
52 if singletons.settings.SECURITY is not None:
53 checker_class = singletons.settings.load('SECURITY')
54 else:
55 checker_class = DummySecurity
56 checker = checker_class()
57 url_string = querydata['url'][0]
58 foreign_res = ForeignResource(url_string)
59 foreign_res.validate() # TODO move domain checks into this module
60 await checker.check(typestring, querydata)
```

Start with security.py around check() and the TODO for moving domain checks, then inspect utils/urls.py and ForeignResource. Determine how URL reversal and the configured SECURITY checker should interact; done means domain checking is integrated there, URL reversal is supported, and the active security implementation is respected.

Written by the indexing model from the issue text.