feat: Improve UX to match new mockups

Uses new API features for preview, deleting, pinning, and closing. Refactors and improves styling to match new mockups.
Adds the new post filter bar element.

src/discussions/posts/data/slices.js

@@ -22,6 +22,7 @@ const threadsSlice = createSlice({
     threadsById: {
       // Mapping of threads ids to threads in them
     },
+    author: null,
     pages: [],
     threadDraft: null,
     nextPage: null,
@@ -43,6 +44,10 @@ const threadsSlice = createSlice({
       state.status = RequestStatus.IN_PROGRESS;
     },
     fetchThreadsSuccess: (state, { payload }) => {
+      if (state.author !== payload.author) {
+        state.pages = [];
+        state.author = payload.author;
+      }
       state.status = RequestStatus.SUCCESSFUL;
       state.pages[payload.page - 1] = payload.ids;
       state.threadsById = { ...state.threadsById, ...payload.threadsById };
@@ -143,6 +148,10 @@ const threadsSlice = createSlice({
     },
     setSearchQuery: (state, { payload }) => {
       state.filters.search = payload;
+      // Search doesn't work with following
+      state.filters.status = state.filters.status === PostsStatusFilter.FOLLOWING
+        ? PostsStatusFilter.ALL
+        : state.filters.status;
       state.pages = [];
     },
     showPostEditor: (state) => {