Doc: Made QDoc Manual use Qt 5's qdoc

-removed extra qdocconf and files
-"make docs" using QMAKE_DOCS
-installs the documentation in QT_INSTALL_DOCS
-updated title of the manual to "QDoc Manual"
-modified listing of contents in Assistant

Change-Id: I22f93c0903c5e672a0e7efa83bf3f592658be66d
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Fixed QT_NO_DRAGANDDROP build for the windows plugin

Change-Id: Ieb987105bdcc08118a1b83cf3b74a93fa402264a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Fix spelling error found by bot.

Change-Id: I7e9a00e014368450b6dcb8172f7888bb744d6555
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>