Redesign & restructure conversation settings

[julian-wls]

Problem Description

Currently, the conversation settings look a little bit cluttered and unstructured and the elements are quite separated from each other.

Solution

There should be a redesign to align the settings screen more with the iOS app and make it visually more appealing by introducing sections.
This PR should also include small adjustments to the browse channels screen and maybe introduce a search bar there as well.

Additional context

This should happen as a follow up of #363 and #362, where some views related to the conversation settings have already been adjusted.