Don't auto finish transactions

[jamesmontemagno]

Give ability to turn it on though if we want to for back compat for non-consumeables.

Please take a moment to fill out the following:

Fixes #414.

Changes Proposed in this pull request:

• Add back compat to auto finish ios transactions
• Consume on iOS now calls Finish
• Finish still finishes on iOS, but would need to be called for all of them

[edgiardina]

It's been a while since I've had this top of mind, so forgive me if the answer is obvious, but shouldn't we just finish all non-consumable transactions automatically, and if the product is consumable on apple, then Finish the transaction when ConsumePurchaseAsync is called, like in android? Or am I missing something?

[jamesmontemagno]

Yes, I would have to know if your transaction is consumable or not... else maybe I pass in a flag... let me see here

[jamesmontemagno]

The other ting is that I also Finish all transactions on restore as well as that was a recommended pattern...

[jamesmontemagno]

Alright... so check the code now...

I introduced a new ItemType of Consumable. If it is consumable then we don't autofinish the transaction.

Now on restore it is tricky. I am goign to make the getpurchases take in a list of ids not to finish. so a bit of work, but I think smoother

[jamesmontemagno]

@edgiardina now finished with the implementation. let me know what you think there.

I also updated documentation