I18N in nicknames / channel names support

[strlcat]

Hey,

Since most of code that handles nicknames and channel names here is Python character clean, I propose to lift current restriction to permit only ASCII 7bit names and allow any valid UTF-8 sequences, since Python transparently deals with them.

Tested & working correctly on my fork.

[Y4kuzi]

I increased the allowed characters in 43cc960.
There are still some restrictions but I think most characters are covered now.
Let me know if you encounter any issues.