Add QUuid::toRfc4122() and fromRfc4122()

Add QUuid::toRfc4122() and fromRfc4122()

Following the RFC4122, provide the interfaces between QUuid
and QByteArray, they are simpler then toByteArray() and
relevant.

Thanks for the suggestion and brief code from Robin Burchell.

Task-number: QTBUG-19420
Reviewed-by: joao
(cherry picked from commit 06873e467d98ad60d827afae29500bf2ff783c03)

Change-Id: I4623ae3363f1d5affa45de73fac616bb67a9eaa1
Reviewed-on: http://codereview.qt.nokia.com/168
Reviewed-by: Liang Qi <liang.qi@nokia.com>