List signed-up bloggers

Prints out a list of all the bloggers registered on the platform ordered by the number of posts they've made.

The query itself is an ORM hack that works. I don't know if it's good as a SQL query or not, but for checking up on the two users currently registered on commit--blog it's just fine. Here is the SQL it generates

```sql
SELECT blogger.id AS blogger_id, blogger.gh_id AS blogger_gh_id, blogger.username AS blogger_username, blogger.name AS blogger_name, blogger.avatar_url AS blogger_avatar_url, blogger.access_token AS blogger_access_token
FROM blogger ORDER BY (SELECT count(blogger.id = commit_post.blogger_id) AS count_1
FROM commit_post)
```

That `ORDER BY (SELECT count...` makes me nervous; it seems like it's doing a lot of work. Then again the python code felt like it would be a lot of work too:

```python
bloggers = Blogger.query \
                .order_by(db.session.query(
                    func.count(Blogger.commit_posts)))
```

I'd like to spend some more time learning and writing SQL queries. Not that I ever work with enough data for my fumbling ORM hacks to matter, but I'd like to have a more clear picture of what is going on. Maybe some day I'll have enough data to play with for it to matter.

My impression of `SQLAlchemy` is that, given knowledge of how to write good queries, it makes expressing them pythonic and doesn't get in your way. Not that I have experience to know, but for now that's why I'm still using it, given how easy it makes getting data in and out.