Add explanation to mute dialog, refactor and clean up mute/block UI (#11992)

* Add some explanation to the mute modal dialog

* Remove `isSubmitting` from mute modal code, this wasn't used

* Refactor block modal

Signed-off-by: Thibaut Girka <thib@sitedethib.com>

* Refactor SCSS a bit

* Put mute modal toggle to the same side as in the report dialog for consistency

* Reword mute explanation

* Fix mute explanation styling

* Left-align all text in mute confirmation modal

app/javascript/mastodon/reducers/blocks.js

@@ -0,0 +1,22 @@
+import Immutable from 'immutable';
+
+import {
+  BLOCKS_INIT_MODAL,
+} from '../actions/blocks';
+
+const initialState = Immutable.Map({
+  new: Immutable.Map({
+    account_id: null,
+  }),
+});
+
+export default function mutes(state = initialState, action) {
+  switch (action.type) {
+  case BLOCKS_INIT_MODAL:
+    return state.withMutations((state) => {
+      state.setIn(['new', 'account_id'], action.account.get('id'));
+    });
+  default:
+    return state;
+  }
+}