Fixing message recieving from ObjC side.

I discovered a bug when I was trying to use RestoreTransactions functionality.
To be available for calling via ObjC ```UnitySendMessage()```, function must not be static. When trying to send message to static function of MonoBehaviour, we are getting an error like

```
2013-05-27 17:32:58.106 appname[25368:707] [Debug] SOOMLA StoreController: Sending restore transaction request

SendMessage: object Soomla does not have receiver for function onRestoreTransactionsStarted!
```

So:
- Soomla.cs: removed 'static' keywords on several functions that should be available for UnitySendMessage from objc code.