Add the nfc corkboard example

[ChangeLog][QtNfc][General] Added a new corkboard example displaying
the content of NDEF text records.

Change-Id: Ic60ef8a67abaf45b5f34378e822f3d89ca7e26a2
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Misc fixes for the new corkboard example

- The example was hooked into the build system.

- The display location of notes on the display was optimized to reduce
overlapping with the bottom and right corner.

- A documentation page was added for the example.

- example binary added to git ignore list

- Fix license headers

Change-Id: Ib18433c2a7dd68a3573c62ff3215fa0e69954f95
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>