QDoc: Auto-generate signal handler names in \qmlsignal

The QML Documentation Style page (http://qt-project.org/wiki/QMLDocumentationStyle ) says, "Signal documentation must... mention the corresponding signal handler", and gives this example:

/*
    This signal is emitted when the user clicks the button. A click is defined
    as a press followed by a release. The corresponding handler is
    \c onClicked.
*/

This is a good candidate for automatic text generation. Rather than ask developers to write it out manually (which takes extra effort and might be overlooked/wrongly-written), QDoc can append "The corresponding handler is \c on<CapitalizedSignalName>." as a standalone paragraph to the documentation.

Tasks

1. Add this feature to QDoc (including necessary refactoring as required)
2. Remove the lines that have already been added manually
3. Update tests
4. Update the wiki page; no longer ask developers to mention the handler names