Add a jump to time feature

[Flameborn]

Hello,

It would be fantastic if Cog had a jump to time feature, essentially allowing a user to jump to a specific time within the currently playing file in HH:MM:SS format. This would be quite useful to review the end of a file, or could be used as a basic bookmark feature. For example:

1. The user presses a hotkey, e.g. cmd+j, and a window pops up with a field where the current position is pre-filled in HH:MM:SS format.
2. At this point, the user can either copy this and note it down to continue playback from this position, or could enter a new position.
3. After clicking a button to confirm, Cog would jump to the entered position or it would ignore the entered time (if it's greater than the length of the file, etc).