Add mojibake extension

What does the merge request do?

In this MR, I added a new extension called mojibake.

It can intentionally cause mojibake, or correct them by reinterpreting text encodings. This is useful for generating creepy looking text.

Most mojibake converters are web-based, and it cannot support rich text. With this extension, this function can be integrated to Inkscape. And it can even preserve original styles.

Implementation notes

It works by encoding the Python string as bytes, then decoding that with another one into str. The encodings are chosen from GUI that is defined in INX file.

Summary for release notes

Added mojibake: a way to reinterpret text encoding to transform text in unusual way.

Checklist

• Add unit tests (if applicable)
• Changes to inkex/ are well documented
• Clean merge request history