Add CONFIG_CLASS_MAGIC; enhance super_string

The CONFIG_CLASS_MAGIC configuration option controls whether the Object API
performs a check for the presence of a struct class_base in a template it
creates an object from. This is particularly useful as I often find myself
debugging some weird memory corruptions where I just forgot to add this
structure.

I have to remember to add a .config file to the build process.

The super_string sample module manipulates the strings' reference count and
uses timers of 1 second ticks to display the string dying once a second.