Template for all sidebars

[MarskyMessier]

Sidebar are currently a hassle to deal with if there's any customization needed past css (where you'd need actual html wrapper etc), having a template akin to admin (?) where sidebar links are stored in a config file and there's only one common html but each sidebar has its links grabbed from the config.

Unsure how long or annoying it'd be, but given it's a breaking change, having it on v4 would be a huge QOL update for front-end devs!

[itinerare]

Given that sidebars are a pretty big area of redundancy, it makes a lot of sense to me and probably won't be that much of a hassle to implement-- just a breaking change, yeah.