Add python stringifiers for database objects

They're a little bit nicer to work with in the shell now.
Show blogger.username when blogger.name is not available

So I promised my friend @rileyjshaw a link to this blogging platform yesterday, but I kept putting it off so that I could try to get it into a usable state first. Finally earlier this evening I sent him a link. I took a break, came back, and checked the logs to see if he'd signed in yet or not. Sure enough he had!

Excited, I went over to [Riley's page](http://rileyjshaw.commit--blog.com), and was greated by my website as it would have greeted Riley:

    $ commits-by "None"

    No posts by None yet :(

Riley has not entered a name for his github account. Riley, if you felt saddened by that page you have only yourself to blame :)

It's fixed now.