[Gemini] Prevent multiple set initial value assertions for same resource

Gemini currently allows Cygnus games to have multiple initialize(set_value(..)) assertions for the same resource (with both same and different values). Should prevent this. 

e.g., in beach_1.lp:
```
initialize(set_value(resource(r_1_XX_),scalar(0))).
...
initialize(set_value(resource(r_1_XX_),scalar(0))).
initialize(set_value(resource(r_1_XX_),scalar(1))).

```