refactor(handlers): Use rendering actor for page renders

This currently breaks error handling in page render flows. To fix it
properly, the database actor should return failable futures instead of
`Result<T>` wrapped in a future.

todo.org

@@ -1,4 +1,7 @@
+* DONE Pin *-versions in cargo.toml
 * TODO Configurable number of DB workers
-* TODO Pin *-versions in cargo.toml
 * TODO Match certain types of Diesel errors (esp. for "not found")
 * TODO Sketch out categories vs. tags system
+* TODO Markdown support
+* TODO Quote button
+* TODO Multiquote buttons