Displaying a login alert on AEFClient init

Starting the OctoKit authentication logic by
displaying a login alert view
Adding AEFUser class

Adding a class to represent Github users with username
and password
Inheriting AEFUser from MTLModel
Adding AEFUserCache

* Adding SSKeychain to the project
* Implementing the AEFUserCache to cache AEFUser objects using
  the keychain
Implementing AEFUserCache logic in AEFClient
Correctly linking the sample project with RC
Removing hard coded vendor path from sample project
Adding AEFClient authentication callback block
Adding a PLCrashReport category
Updating Makefile to use xctool
Adding before_install phase to travis.yml
Upgrading xctool before install
Fixing failing user cache test
Implementing basic Issue creation

Updating PLCrashReport category to return some dummy params
Sending a request with the authenticated client
Displaying login on failed authentication
Implementing github token caching

Ditching the password caching to use the recommended
GitHub client token caching, this allows for better auth
and security.
Implementing one time password handling

* Now handling one time passwords correctly
Adding AEFClient Private header
Moving error handling out to it's own method
Removing authenticated BOOL from authenticate block