Doc: describe translation sources in Developer topic
Doc: describe translation sources in Developer topic

Move information from the Release Manager topic and
add information about QML sources in the Qt Linguist Manual.

Change-Id: I0d2a2ea68a2e7e94895b41436d9f973d8c2cb2aa
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