Some corrections to English UI text (#506)

* Update some UI strings for more natural English

* Correct message text

* Correct message text

* Update the strings everywhere

Because they are also used as base messages for other languages

templates/posts/details.rs.html

@@ -38,7 +38,7 @@
             <a href="@uri!(posts::edit: blog = &blog.fqn, slug = &article.slug)">@i18n!(ctx.1, "Edit")</a>
             &mdash;
             <form class="inline" method="post" action="@uri!(posts::delete: blog_name = &blog.fqn, slug = &article.slug)">
-                <input onclick="return confirm('Are you sure you?')" type="submit" value="@i18n!(ctx.1, "Delete this article")">
+                <input onclick="return confirm('@i18n!(ctx.1, "Are you sure?")')" type="submit" value="@i18n!(ctx.1, "Delete this article")">
             </form>
         }
         @if !article.published {

templates/posts/new.rs.html

@@ -35,7 +35,7 @@
         <textarea id="editor-content" name="content" rows="20">@Html(&form.content)</textarea>
 	    <small id="editor-left">@content_len</small>
         <p>
-            @i18n!(ctx.1, "You can upload medias to your gallery, and copy their Markdown code in your articles to insert them.")
+            @i18n!(ctx.1, "You can upload media to your gallery, and copy their Markdown code in your articles to insert them.")
             <a href="@uri!(medias::new)">@i18n!(ctx.1, "Upload media")</a>
         </p>