Hi-Density cache usage examples

**HiDensity cache usage examples:**
* HiDensity cache Put/Get/Remove usage example
* HiDensity cache TTL usage example
* HiDensity cache Iterator usage example
@jerrinot **AllowUnsafe** is not about Off-Heap storage, it is just about global serialization in all Hazelcast. It is advised to use it because you want no more GC since you are using Off-Heap cache. It is not necessary but it is a good practice for Off-Heap cache usage. So, I think without removing it, adding comment and making it configurable should be better.