tutorial: add first start screen

Signed-off-by: Blechd0se <alex.christ@hotmail.de>
memory: add trim support for /system

Since the latest 2.6.32 Kernel changes (and on 3.0
probably too) we are able to trim /system

Just add it to the trim menu and call remountSystem()
before we do the operation, since /system needs
to be mounted readable.

Signed-off-by: Blechd0se <alex.christ@hotmail.de>