* Don't inherit from Core::Object everywhere, that's overkill. Use
RefCounted instead.
* Change some constructor visibilites to facilitate the above.
* default-implement all virtual destructors if possible.
* Drive-by include hygiene.
Derivatives of Core::Object should be constructed through
ClassName::construct(), to avoid handling ref-counted objects with
refcount zero. Fixing the visibility means that misuses like this are
more difficult.
This commit is separate from the other Applications/Libraries changes
because it required additional adaption of the code. Note that the old
code did precisely what these changes try to prevent: Create and handle
a ref-counted object with a refcount of zero.
