[Glitch] Add explanation to mute dialog, refactor and clean up mute/block UI

app/javascript/flavours/glitch/actions/blocks.js

...javascript/flavours/glitch/containers/status_container.js

.../features/account_timeline/containers/header_container.js

...h/features/status/containers/detailed_status_container.js

app/javascript/flavours/glitch/features/status/index.js

...ipt/flavours/glitch/features/ui/components/block_modal.js

...ript/flavours/glitch/features/ui/components/modal_root.js

...ript/flavours/glitch/features/ui/components/mute_modal.js

app/javascript/flavours/glitch/reducers/blocks.js

app/javascript/flavours/glitch/reducers/index.js

app/javascript/flavours/glitch/reducers/mutes.js

app/javascript/flavours/glitch/styles/components/modal.scss

...avascript/flavours/glitch/styles/mastodon-light/diff.scss

app/javascript/flavours/glitch/util/async-components.js