Add 'Topics' page to show latest root posts

Problem: @masukomi pointed out that the 'latest' view doesn't show the
awesome slice of content that you'll see if you just look at root posts.

Solution: Let's experiment with them! This commit adds a 'Topics' page
that has the latest root posts from people you're following.

src/index.js

@@ -121,15 +121,15 @@ router
     ctx.body = await publicPopular({ period });
   })
   .get("/public/latest", async ctx => {
-    const publicLatest = async () => {
-      const messages = await post.latest();
-      return publicView({ messages });
-    };
-    ctx.body = await publicLatest();
+    const messages = await post.latest();
+    ctx.body = await publicView({ messages });
   })
   .get("/public/latest/extended", async ctx => {
     const messages = await post.latestExtended();
-
+    ctx.body = await publicView({ messages });
+  })
+  .get("/public/latest/topics", async ctx => {
+    const messages = await post.latestTopics();
     ctx.body = await publicView({ messages });
   })
   .get("/author/:feed", async ctx => {

src/models.js

@@ -679,6 +679,44 @@ module.exports = cooler => {
 
       return messages;
     },
+    latestTopics: async () => {
+      const ssb = await cooler.connect();
+
+      const myFeedId = ssb.id;
+
+      const options = configure({
+        type: "post",
+        private: false
+      });
+
+      const source = await cooler.read(ssb.messagesByType, options);
+
+      const extendedFilter = await socialFilter({
+        following: true
+      });
+
+      const messages = await new Promise((resolve, reject) => {
+        pull(
+          source,
+          pull.filter(
+            message =>
+              typeof message.value.content !== "string" &&
+              message.value.content.root == null
+          ),
+          extendedFilter,
+          pull.take(maxMessages),
+          pull.collect((err, collectedMessages) => {
+            if (err) {
+              reject(err);
+            } else {
+              resolve(transform(ssb, collectedMessages, myFeedId));
+            }
+          })
+        );
+      });
+
+      return messages;
+    },
     popular: async ({ period }) => {
       const ssb = await cooler.connect();
 

src/views/template.js

@@ -46,6 +46,7 @@ module.exports = (...elements) => {
           li(a({ href: "/public/latest/extended" }, "🗺️ Extended")),
           li(a({ href: "/" }, "📣 Popular")),
           li(a({ href: "/public/latest" }, "🐇 Latest")),
+          li(a({ href: "/public/latest/topics" }, "📖 Topics")),
           li(a({ href: "/profile" }, "🐱 Profile")),
           li(a({ href: "/mentions" }, "💬 Mentions")),
           li(a({ href: "/inbox" }, "✉️ Private")),