Timer class changes -- more cleanly separate ticks versus seconds.

Many methods that returned seconds now have a second variety that returns raw ticks. This is helpful because ticks are an integral type that can be atomically added to a statistic, whereas double (seconds) values are more of a pain.

This really doesn't change the existing interface (hence, no changes anywhere in the codebase to uses of Timer, only to the implementation). But it allows new uses that retrieve the ticks rather than the seconds.