Cleanup imports in bridgedb.HTTPServer.

  * CHANGE all objects named `resource` to something more specific,
    otherwise we cannot do `from twisted.web import resource`.
More import cleanups for HTTPServer.

 * CHANGE `from twisted.web.server import Site` to import the entire
   `server` module instead.
A couple PEP8 whitespace fixes in docstrings for HTTPServer.
Change ReCaptchaProtectedResource.checkResponse() to also return request.

We need to return the original request, not just the boolean
representing the validity of the CAPTCHA solution, if we want to be able
to interact with the original request while rendering it.
Add ReCaptchaProtectedResource._renderDeferred() to render deferred resources.
Change ReCaptchaProtectedResource.render_POST() to call _renderDeferred().

 * FIXES #11218 (again).
Add coverage pragma lines to blanket excepts in HTTPServer.

They are gross, but we have to have these general excepts everywhere,
otherwise users could be shown a traceback.
Add a docstring and comment to checkResponse() in ReCaptchaProtectedResource.
Remove a superfluous error message about gettext files.
Add --rcfile option to additional coverage lines in Makefile.
Remove gimp captcha unittest code from recaptcha unittest setUp().
Add unittests for _renderDeferred().
Change checkSolution() unittest to check for tuple.
Change unittests for reCaptcha render_POST() to check NOT_DONE_YET.
Merge branch 'hotfix/11218-async-render' into develop
Add unittests for HTTPServer.WebResourceOptions.