Runtime support for Script Group as single module

Also made two other cleanups:
- Changed KernelID/InvokeID into IDBase in class Closure
    Rather than having two fields in class Closure, one of type ScriptKernelID and
    the other InovkeID, use a single field of the common base class IDBase. Added a
    boolean field to indicate whether it is kernel or invoke, since -fno-rtti is on.
- Removed user pointer from CPU closure

Change-Id: I5553f86b2e58325f85649078d48685a38f12d62f
8 files changed