Doc: Document signals (not handlers) under \qmlsignal

Append the handler names to the end of the corresponding signal doc.

Task-number: QTBUG-35846
Change-Id: I3d627ba7ed5be94e5c402ab092b4d582536499e8
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Doc: Fix broken \qmlsignal links

Fix the breaks caused by the re-categorizing of \qmlsignal pages

Task-number: QTBUG-35846
Change-Id: I528ae16ec522fc902133e22d8f53c87a7f0d56ad
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>