Show categories in hierarchy

[khyurri]

Currently, categories in BadgerDoc are displayed as a plain list with pagination. We need to change this to a hierarchy view.

Back-end

Assumptions:

• We don't expect thousands of categories per tenant in one installation; if versioning is required, the taxonomy microservice can be used for this purpose.
• We should be able to retrieve the entire hierarchy of categories for a tenant using a single request.

In the back-end, we need to add a GET all categories endpoint. This endpoint must return the same format as the currently used /search endpoint, but without pagination information.

Front-end

• Change the table view to a tree view. Initially, all categories should be expanded and the interface should display the hierarchy of categories.
• Change the colors in the 'Choose colors' popup. Most of the current colors in the palette are too light and thus unusable. It would make sense to add more dark colors and remove lighter ones.