Fix blog index/tag pages lacking titles

[preaction]

For metadata purposes, it's important for every page to have a descriptive title. Every page in the blog index should have a title, and every tag page should have a title. The titles should look as follows:

• /index.html - <title><%= $app->title %> - <%= $site->title %></title>
• /page/2/index.html - <title>Page 2 - <%= $app->title %> - <%= $site->title %></title>
• /tag/{tag}/index.html - <title>{tag} - <%= $app->title %> - <%= $site->title %></title>
• /tag/{tag}/page/2/index.html - <title>Page 2 - {tag} - <%= $app->title %> - <%= $site->title %></title>

To achieve this we will need multiple things:

1. All applications will need a title attribute (add a title attribute to Statocles::App role)
2. The paginator (Statocles::Page::List->paginate) will need to set titles for all the pages it generates. It should accept an initial title for the first (index) page, and then add "Page #" to all subsequent pages