Add file hiding and uosc actions

[po5]

Tested with uosc and vanilla menus.
mpv-menu-plugin untested but I shouldn't have broken anything.

This adds shift+enter/click for appending to playlist, and del for hiding entries. Feature parity in vanilla and uosc menus.

uosc action bindings could be made configurable, but I prefer to keep them hardcoded to be consistent with uosc's builtin menus.

Note this does not hide future entries, this is on purpose.
Manually reopening a file that was previously hidden will display new entries for it like with any other file.

The downside of using uosc's callback mode is that our script needs to be idle to handle all item activations.
If the page is still loading e.g. in a search that returns fewer than options.entries on a large log file, the user cannot click on files that are already shown to load them, until the page fills up or we reach the end of the log.
I still want to decouple a log loading slave script from primary menu logic before adding features that exacerbate this issue, which is why this isn't in the main branch for now.

uosc versions prior to 5.3.0 are still supported.

Closes #34, cf. #7

[uugaabuugaa]

Thank you for doing this. However I faced a small issue. Sometimes pressing Del or clicking on hide button instantly vanishes the entry and sometimes it doesn't and will show it as hidden once I restart memo history (not mpv). I don't why this inconsistency is occuring tho.