X11: field name is UTF-8 encoded

According to the wm-spec[1] the name field is UTF-8 encoded. Therefore
it should be decoded before being used.
[1]: http://standards.freedesktop.org/wm-spec/1.3/ar01s05.html
Add UTF-8 encoded name test
Merge pull request #5 from pstuifzand/utf8-app-name

X11: field name is UTF-8 encoded