[#2457] Fix unknown encoding cp65001 error on Windows.

Problem
-----

On windows machines after running the server (fixed in the meantime) and/or running the testsuite an error is printed on any subsequent Python command:

```
LookupError: unknown encoding: cp65001
```

Changes
-----

Added `cp65001` as an alias for `utf_8`.

How to test
-----

reviewers @adiroiban

Please check that the code changes make sense. Once you approve I will generate a new distribution and replace the existing one.

I've tested the changes on my local machine and they work as expected.