layout : main : Use RelativeLayout instead of LinearLayout and make fbLoginButton centered within it's parent
layout : main : Add com.facebook.widget.ProfilePictureView and set the login button to be displayed below it
FacebookAccountLoginActivity: Create ProfilePictureView field and have it reference ProfilePictureView in layout
FacebookAccountLoginActivity: Add code to display profile pic when logged in, and hide it when logged out
FacebookAccountLoginActivity: Make class final, no inheritance intended
layout : main : Move profile picture to centre of activity, have login button show up right underneath it, centred horizontally
Add TODO for handling screen rotation in FacebookAccountLoginActivity
FacebookAccountLoginActivity: Add TODO about displaying Facebook user's name