Minor changes to O2

I've done some minor changes to O2, mostly to familiarize myself with your code and github! :) They don't change any functionality and whatever changes I have done have been tested against Twitter with my example client.

I'm summarizing the changes here (also in commit msg):

* Changed allocation of SimpleCrypt from heap to stack. This simplifies its use a little as we don't need to keep track of construction and deletion.
* Removed manual deletion of QNAM as it's parent is already set and Qt will take of deleting children when parent is deleted.
* Added a helper function for generating the key to be used for encrypting/decrypting stored tokens.
* Simplified concatenation of lists in getRequestBase().
* In O1::onTokenRequestFinished(), added extra check to if "oauth_callback_confirmed" is set to true. This is required by RFC 5849 (section 2.1) and is also menioned in the Twitter API docs here: https://dev.twitter.com/docs/auth/implementing-sign-twitter

Let me know what you think.

-mandeep