Supporting new StoreController optimizations in android-store and ios-store

- Removed the need to call ‘StoreOpening’ and ‘StoreClosing’
- (optional) Added ‘startIabServiceInBg’ and ‘stopIabServiceInBg’ for
cases that you have a storefront and you want Iab service to be open in
the background (while the storefront is open)
Added instructions to support the removal of storeOpening and storeClosing
Added instructions to support the removal of storeOpening and storeClosing
Merge branch 'master' of github.com:soomla/cocos2dx-store

* 'master' of github.com:soomla/cocos2dx-store:
  removed "androidTestMode" from README.md
  Update README.md