refactor the algorithm for testing the cors

while here:
- send cors headers even if the status is 404
- add: access_control_expose_headers config option - list of additional headers sent in Access-Control-Expose-Headers
- add: access_control_allow_credentials config option - if true return Access-Control-Allow-Credentials header equal "true"

winixd/core/config.cpp

@@ -353,6 +353,8 @@ void Config::AssignValues()
 
 	allow_all_cors_origins = Bool(L"allow_all_cors_origins", false);
 	ListText(L"allowed_cors_origins", allowed_cors_origins);
+	ListText(L"access_control_expose_headers", access_control_expose_headers);
+	access_control_allow_credentials = Bool(L"access_control_allow_credentials", false);
 }