Headers are ignored

This code does not work when run on the CLI, which poses a problem when trying to write tests which send headers.

https://github.com/Codeception/util-universalframework/blob/f9da1f81c8c54c8edefc1bf7faf77be662ffb7eb/src/Codeception/Lib/Connector/Universal.php#L54-L69

From what I can tell the `header()` function on the CLI does absolutely nothing so the headers are not stored for later retrieval.

There are a few other problems with this code like it always returns a 200 response code, headers are case insensitive which could break the `isset()`, the same header can be sent multiple times so only the last one will be kept by this code.