chore(posters): merge GEWISPosterHandler and HubblePosterHandler into new CarouselPosterHandler

[Yoronex]

Description

This PR merges the two separated poster handlers (GEWIS and Hubble) into one, unified "Carousel" poster handler. The primary goal is to unify the codebase for the handlers that rotate a deck of slides (a carousel), but still keep it versatile so custom stylings can be applied for different organizations. This PR therefore includes the following changes:

• Refactored the GEWISPosterHandler into the new "CarouselPosterHandler".
• Remove the HubblePosterHandler.
• Added new server settings to change the most basic features of the progress bar. Think of color of the slider, the logo in the corner, whether the clock ticks, whether borrel mode is present, etc.
• Added support for a custom CSS file to be uploaded as server setting, which can be used to completely redesign the progress bar. Any CSS properties put in that file will override the default configuration. The example stylesheet (with some CSS in there) can be found here: https://github.com/GEWIS/aurora-client/blob/chore/refactor-gewis-hubble-poster-layouts/src/handlers/poster/poster.css.
• Added new endpoints for the subscribers to fetch the settings, logo svg and CSS stylesheet.
• Reorganized all poster handler endpoint, so the probability of conflicts is decreased.

Related issues/external references

Types of changes

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Style (Change that do not affect the functionality of the code)