Doc: Fixed some uses of terminolgies in qdoc files.

-"element" -> "type" or "object" (not in all cases where this change applies)
-some instances of QtQuick. It should be "Qt Quick".
-only in qdoc files. Examples and source code changes will be done later.

Task-number: QTBUG-30180
Change-Id: Ie587461a138e97606f761ad1e90909c91b479303
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>