Eliminate warnings / clean up and simplify code

[chanseokoh]

I had this code clean-up hanging around for a while.

A few points in this code clean-up:

• connected has always been true, so it's essentially meaningless.
• Removed the private method checkLoggedIn(), which automatically pops up a login browser if no one is logged in. It wasn't compatible with the login flow using a local server, so it shouldn't be used anyway. For the existing places where checkLoggedIn() is used, I enforced the precondition that the class should be in a logged-in state.
• There had been mixed use of GregorianCalendar().getTimeInMillis() and System.currentTimeMillis().
• Changed method names to eliminate confusion.

@nbashirbello @elharo @briandealwis @akerekes

[briandealwis]

LGTM. The listeners weren't thread safe to begin with. But I wouldn't complain if you came up with a better method name than logInHelper()!