Doc: Renamed "QML Application Developer Resources" to "QML Applications".

-original title usually shortened in visible text
-"QML Applications" is more generic and easier to remember.

Change-Id: Ie4c1334475f0f9acbdd3114811cbffcf5954fd5d
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>