Enable automatic tag polling if message handler is not supported.

All examples have used message handler registration so far. That's
not always supported on all platforms. Neard is one of those
platforms against which this this was verified.

This patch converts some examples to use manual target detection
if handler registration fails.

Change-Id: Icfd8b7c695e63351a45b867fd69e9fc5fefb9360
Reviewed-by: Martin Leutelt <martin.leutelt@basyskom.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>
QML NearField type never emitted tagRemoved() signal

Change-Id: I7c6127b6f941bd5623cb6e01bd9db9063afaedd6
Reviewed-by: Martin Leutelt <martin.leutelt@basyskom.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>
Fix corkboard example display

1.) The z order of the sticky notes and the corkboard image
was totally off. Most likely this is due to a bug in QtQuick's
ListView implementation. Now we have a strict parent child relationship
which seems to work.

2.) The tag content was always empy. This was due to incorrect usage
of QML NdefRecord API usage.

Change-Id: I67e9e42e842f1cb051ef62d481b99b3c7b97718c
Reviewed-by: Martin Leutelt <martin.leutelt@basyskom.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>