Playhead movement is choppy

[Jonathan Thomas]

The playhead (i.e. the red line) is only updated a few times a second, which creates a choppy motion. Also, seeking to a new position on the timeline just jumps the playhead, instead of animating to it's new location.

[Jonathan Thomas (jonoomph)]

Animated the play-head and play-head line to the cursor position when the
ruler is clicked. When the ruler is dragged (i.e. scrubbed) it does not animate.
Also, when the video is playing, it does not animate. This is to prevent uneven
and stuttering play-head movement. But in general, whenever
a drag operation on the ruler is started (or a click) the play-head smoothly animates
the position of the cursor. I really like the way it feels.

Also, sped up the delay in the video thread. This results in higher CPU, but
smoother play-head movement as it moves across the timeline.

[Jonathan Thomas (jonoomph)]

Also... Improved the animation of the play-head. Now the play head moves silky smooth
when the video is playing.