Make blog more SEO-friendly

Adds optional `metaDesc` field to blog create/edit form, and edits routes to allow dynamic setting of page titles and descriptions for the [ms-seo](https://github.com/DerMambo/ms-seo) package.

Description for the `blogIndex` template (the blog index and the tag pages) can be set on the client-side using `Blog.config()`

Addresses #93