License files should be read as utf-8 files

Right now, default codec is used (codec for current locale) which is wrong, as i think. Codec for my locale on windows is cp1251, however in linux it can be utf-8, correct me if i'm wrong.
Anyway, while developing cross-platform app, i prefer to use utf-8 encoding in files instead of other specific encodings.
Here's a fix that chooses utf-8 codec for license files https://codereview.qt-project.org/#change,45647