optional Authorization Code Flow

[moooji]

No description provided.

[digitaldavenyc]

@moooji This is awesome. I'm going to test it tomorrow and will let you know if there are any issues. I do have some concerns because there is an outstanding bug #6 that could have implications on this PR. Further changes may be required after that bug is fixed.

[digitaldavenyc]

Is this intended to be a starting point for using the beta 23 sdk? Including it sets off a lot of errors on other functions not related to auth.

[moooji]

No this PR should not have to do anything with SDK 23. As you can see in the changes, I have only added "tokenSwapURL" and "tokenRefreshURL" in spotifyModule/ios/SpotifyAuth.m. This should compile without problems with SDK 17.

[moooji]

I have also renamed SpotifyModule -> SpotifyAuth in README, because SpotifyModule does not exist and seem to be some legacy code?

[viestat]

I really like using an object with options for Auth, awesome job!
I need you to change a couple things before I merge this. it would be nice to only set tokenSwapURL and tokenRefreshURL only if the user provides them, so maybe add a condition for that.
In the README file, please change back SpotifyAuth to SpotifyModule as I will change it in the code too.
Please forgive the late review but I have been super busy this past month.
Thank you so much for your contributions and your patience!