Refactor "Navigation" Plugins Category

[chrisgrieser]

In my view, the Navigation plugin category is a bit of a mess. some plugins are for navigation between notes, from for navigating inside one note, some plugins are for some sort of navigation that is neither.

The category would benefit from some clearer definitions / splitting and subsequent refactoring of plugin assignments.

[argenos]

I'm removing the label until we have an idea of what the new categories should be, otherwise it's going to be a lot of brainstorming and asking for changes from the (potentially a new) contributor who tackles this.