Doc: replace "Qt APIs" with "Qt libraries"
Doc: replace "Qt APIs" with "Qt libraries"

Change-Id: I1af600391fb95e2dbcdba9ae37e40837d34d9add
Reviewed-by: hjk <6fac1c92f5b9c7890a04d7f8a9d8912d16355eac@ovi.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc