Don't redirect dynamic CSS from https to http

This can break things (d'uh).

Do this by introducing a new decorator, @ssl_optional. When this is
present, no SSL redirection will happen, regardless of whether the
access comes in over http or https.

This decorator overrides @ssl_required, but for redability's sake,
never use both at the same time.

pgweb/util/decorators.py

@@ -8,6 +8,13 @@ def ssl_required(fn):
 	# wraps retains original function attributes such as __name__, csrf_exempt, etc
 	return wraps(_require_ssl)(fn)
 
+def ssl_optional(fn):
+	def _optional_ssl(request, *_args, **_kwargs):
+		return fn(request, *_args, **_kwargs)
+	_optional_ssl.ssl_optional = True
+	# wraps retains original function attributes such as __name__, csrf_exempt, etc
+	return wraps(_optional_ssl)(fn)
+
 def nocache(fn):
 	def _nocache(request, *_args, **_kwargs):
 		resp = fn(request, *_args, **_kwargs)