Don't safelog randomly generated IPs.

 * REMOVE calls to `Util.safelog` which masked the IP addresses which
   are randomly generated in
   `HTTPServer.CaptchaProtectedResource.render_POST()`. These random IPs
   are sent to the ReCaptcha server in order to not reveal the client's
   real IP, and they are no more revealing/identifying of a particular
   client than the `twisted.web.http.Request.args` which are logged.
Make log message for strange X-Forward-For headers clearer.
Split a long string of chained method calls into separate calls.

 * CHANGE a line in HTTPServer.CaptchaProtectedResource which chained
   several method calls together inside a return statement, into a
   separate lines for each call.
Fix a misnamed logger call in HTTPServer; change severity level.
Catch error case in HTTPServer where ReCaptcha image is None.
Add Sphinx docstring to CaptchaProtectedResource.render_POST().
Preserve HTTP POST args across redirects.

 * FIXES #10737, an issue where if a CAPTCHA was entered incorrectly, the
   client would be redirected back to /bridges.html without the original HTTP
   POST arguments (which specify the requested pluggable transports, IP
   version, etc.).
Fix indentation level in method docstring.
Fix typos in two docstrings in HTTPServer.
Merge branch 'fix/10737-post-args-redirects' into develop
Implement a simple error page to replace all webserver tracebacks.

 * ADD HTTPServer.replaceErrorPage() function for catching templating
   errors and sending them to the logger. The user is served a very
   simply "Somthing went wrong page".
 * CHANGE all calls to mako.templates.Template.render() to be wrapped in
   a try/except block which directs to the new
   HTTPServer.replaceErrorPage() function.
Merge branch 'fix/6127-simple-error-page' into develop
Add Sphinx docstring to CaptchaProtectedResource.render_GET().
Fix Accept-Lang: header log message to actually log the top five LC codes.