PleromaFE Mutes rework

PleromaFE mutes are just a trick to collapse the posts in the PleromaFE. This is confusing and inconsistent as a mute in the MastoFE or using any mobile app (iOS/Android) produces different results: actual timeline filtering happening in the backend.

The mutes in PleromaFE should be re-engineered to synchronize with the way mutes happen in the Mastodon API we support for consistency.

A broader discussion is if the community cares about the way Mutes currently work in PleromaFE and if we should keep them around perhaps as a "Hide" functionality instead. It wouldn't be hard to have both options.