[Feature] Offset markers

[neru2132]

Is your feature request related to a problem? Please describe.
Once sharing markers becomes more commonplace, there might arise a need to be able to move all (or a subset of) markers of a scene in one direction or the other by a fixed offset. This would allow for syncing markers between re-distributions of the same scene or between whole movies and scenes of that movie, for example.

Describe the solution you'd like
Option to change and save the timestamp of all markers by a static offset. Ideally, this would also be possible for a subset of markers. Handling of lower and upper bounds should be considered.

Describe alternatives you've considered
The offset could only be applied in the current session only, without having to write the changes to the database, but I think persisting the values would be preferable in most scenarios.

Additional context
This feature would be very similar to the offset function many video players offer for subtitles.