Add support for remote interact (#519)

Add support for remote interaction ([this thing](https://eldritch.cafe/users/Barmaid/remote_follow) in mastodon)

- [x] create the endpoint dispatching remote interactions to local pages
- [x] add this endpoint to web-finger
- [x] propose remote interaction when following and not connected
- [x] propose remote interaction when liking/sharing and not connected
- [x] propose remote interaction when commenting and not connected
- [x] fetch posts/comments we don't know but remote interaction was requested for ?

templates/posts/details.rs.html

@@ -110,20 +110,23 @@
                 </form>
             </div>
         } else {
-            <p class="center">@i18n!(ctx.1, "Log in, or use your Fediverse account to interact with this article")</p>
+	    <p class="center">@Html(i18n!(ctx.1, "{0}Log in{1}, or {2}use your Fediverse account{3} to interact with this article";
+			format!("<a href='{}'>", uri!(session::new: m = _)), "</a>",
+			format!("<a href='{}'>", uri!(posts::remote_interact: blog_name = &blog.fqn, slug = &article.slug)), "</a>"
+			))</p>
             <div class="actions">
                 <div class="likes">
                     <p aria-label="@i18n!(ctx.1, "One like", "{0} likes"; n_likes)" title="@i18n!(ctx.1, "One like", "{0} likes"; n_likes)">
                         @n_likes
                     </p>
-		    <a href="@uri!(session::new: m = i18n!(ctx.1, "Log in to like"))" class="action">@icon!("heart") @i18n!(ctx.1, "Add yours")</a>
+		    <a href="@uri!(posts::remote_interact: blog_name = &blog.fqn, slug = &article.slug)" class="action">@icon!("heart") @i18n!(ctx.1, "Add yours")</a>
                 </div>
 
                 <div class="reshares">
                     <p aria-label="@i18n!(ctx.1, "One boost", "{0} boost"; n_reshares)" title="@i18n!(ctx.1, "One boost", "{0} boosts"; n_reshares)">
                         @n_reshares
                     </p>
-                    <a href="@uri!(session::new: m = i18n!(ctx.1, "Log in to boost"))" class="action">@icon!("repeat") @i18n!(ctx.1, "Boost")</a>
+                    <a href="@uri!(posts::remote_interact: blog_name = &blog.fqn, slug = &article.slug)" class="action">@icon!("repeat") @i18n!(ctx.1, "Boost")</a>
                 </div>
             </div>
         }