Fetch application description property and Fetch Item references

Adding property  `appDescription` in `PKTApp` class.
Adding `fetchItemReferencesWithID` method in `PKTItem` class.
My bad, you're right. Then I would suggest you use `enumerateWithBlock: ` instead of `pkt_mappedArrayWithBlock:` on line 160 since the mapping method should only be used for when you want to transform the values of an array. It becomes a bit confusing if it is used for plain enumeration. You can still use `pkt_mappedArrayWithBlock` on like 167, since you are transforming the dictionary into an item. Makes sense?