[3.3.x] video player: seek forward by 30s

BP of !687 (merged)

This increases the forward seek step on the swipe gesture to 30s to match the behavior of the previous player as it often requested by users.

We did that in 2013 as we assumed forward seeking a larger step seems to be what most users want, while going back 10s are fine for more granular control.

(cherry picked from commit bf557515) Signed-off-by: Soomin Lee bubu@mikan.io