Doc: Renamed documentation output to "qtassistant" directory.
Doc: Renamed documentation output to "qtassistant" directory.

-project name is qtassistant
-name should match index file for cross linking.

Change-Id: I2f098e3592453185c193a8fbbe97b01dbed50731
Reviewed-by: Leena Miettinen <885fda02d52616fec24ed5fed9b3f0568fce3ead@digia.com>

mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools