Stable icons

There are a few places where $stable_icons is defined, this PR removes all those places and instead creates an always avaliable $context var. Useful for keeping everything under control.

The var was created as earlier as possible to help mods or integrations to be able to use this new var. It also adds a new hook to CRUD the icons, despite my dislike for abusing global scope, it should follow the same pattern as the rest of the hooks.