Add additional buttons to skip forward/back a fixed amount

[AlpyneDreams]

This is what the chapter skip buttons used to do in the original modern. These buttons are added in addition to the chapter skip buttons so you can still skip around in a file with no chapters.

Preview:

Left Mouse Button skips 5 seconds
Shift+LMB can skip 1 frame
RMB can skip 1 minute

These could be made optional with a config setting.

[cyl0]

Looks good, though I think that this should definitely be added as an option rather than a default behaviour as this script aims to mirror the functionality of the default MPV OSC.

[AlpyneDreams]

For sure, I will add a config option. Do you think it should be enabled by default? I think it would be reasonable, since they are present in the default mpv osc's box layout mode.

[AlpyneDreams]

I'll also make the skip amount configurable

[AlpyneDreams]

Done!

Last questions are:

• Do we want to enable them by default (imo I don't see why not, but it's your call)
• Should the button icons have numbers by default (supported for 5, 10, 30). I think the numbers look kind of small to me when not in fullscreen.

[cyl0]

If that's the case then sure, we'lll have it enabled by default.
As for the numbers, I think it would be better to keep them unless the jump amount has been configured to be something other than 5, 10 or 30. The icon without the number isn't very intuitavie as to what it does, so I think it's better off keeping the number even if it's small.

[AlpyneDreams]

Both of those are already the default as of the latest commit so you can go ahead and merge :)

[cyl0]

Great, thanks for contributing!