Created container.h and added more comprehensive hello world

Added a per-container container.h that inclues useful definitions.
Hello world now is in a separate file not to modify main too often.
hello world now prints container name and id.

conts/test/main.c

@@ -5,9 +5,12 @@
 #include <l4lib/arch/syscalls.h>
 #include <l4/api/space.h>
 
+extern int print_hello_world(void);
+
 int main(void)
 {
-	printf("Hello World!\n");
+	print_hello_world();
+
 	return 0;
 }