[Rem]: Moved to YTCommon.h
[Add]: Export read only accesToken property.
[Rem]: Unused code.
[Add]: Fetcher class.
[Rem]: Moved to YTCommon.
[Add]: Completion block to method exchange auth code for tokens.
[Mod]: Correct named dispatch queue.
[Add]: Block for request completion.
[Mod] Replaced code to created block.
[Add]: Use request completion block for exchanging auth code.