Store last seek time in the Flash tech

Instead of caching the last seek time at the player level, cache it in the Flash tech. The only place this value was used was in the progress controls when Flash was loaded, so this simplifies the logic in that component and pushes the hack down into a single location.

I tested seeking on an RTMP stream while paused and noticed that 1 in 5 times, the progress bar incorrectly reports the currentTime. I logged both branches of the currentTime getter in the Flash tech, however, and it appears the incorrect return value is because the SWF is reporting that it is no longer seeking. That says to me that this issue would still exist in 4.3, so things should be no worse than they were before.