- Add blentranslation `BLT_*` module.
- moved & split `BLF_translation.h` into (`BLT_translation.h`, `BLT_lang.h`).
- moved `BLF_*_unifont` functions from `blf_translation.c` to new source file `blf_font_i18n.c`.
Also fix some issues with header files:
- Added ifndef .. define .. endif blocks to be sure headers are not
including twice.
- DO not include WM stuff in headers, use anonymous structure names instead.