Implement proc_ui.rpl + stub SYSSwitchToEManual() to avoid softlocks

- Full reimplementation of proc_ui.rpl with all 19 exports
- Foreground/Background messages now go to the coreinit system message queue as they should (instead of using a hack where proc_ui receives them directly)
- Add missing coreinit API needed by proc_ui: OSGetPFID(), OSGetUPID(), OSGetTitleID(), __OSCreateThreadType()
- Use big-endian types in OSMessage
- Flesh out the stubs for OSDriver_Register and OSDriver_Unregister a bit more since we need to call it from proc_ui. Similiar small tweaks to other coreinit API
- Stub sysapp SYSSwitchToEManual() and _SYSSwitchToEManual() in such a way that they will trigger the expected background/foreground transition, avoiding softlocks in games that call these functions

src/Common/CafeString.h

@@ -20,6 +20,11 @@ class CafeString // fixed buffer size, null-terminated, PPC char
 		return true;
 	}
 
+	const char* c_str()
+	{
+		return (const char*)data;
+	}
+
 	uint8be data[N];
 };