Doc: Adding a "What's New in Qt 5.1" page.

-created a "What's New in Qt 5.0" page to keep 5.0's history.
-featurs taken from http://qt-project.org/wiki/New-Features-in-Qt-5.1

Change-Id: I29d289791ee4195ca545ea793557889809a8e6b4
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>