Added means to search for threads in other containers

Thread ids now contain their container ids in the top 2 nibbles.
Threads on other containers can be addressed by changing those
two nibbles. The addressing of inter-container threads are
subject to capabilities.

src/api/thread.c

@@ -346,7 +346,7 @@ int thread_create(struct task_ids *ids, unsigned int flags)
 		}
 	}
 
-	if (!(new = tcb_alloc_init()))
+	if (!(new = tcb_alloc_init(curcont->cid)))
 		return -ENOMEM;
 
 	/* Set up new thread space by using space id and flags */