Adds a fun console message for people poking around

I noticed we didn't have one of those jovial messages for tech-minded people poking around our dev console. I added something to give it a bit of character.

In Chrome:

![in-chrome](https://cloud.githubusercontent.com/assets/4592/3557683/b2cbb690-0932-11e4-93a3-343a6aea7c8f.png)

In Firefox (Firebug):

![in-firefox](https://cloud.githubusercontent.com/assets/4592/3557685/b59f4c74-0932-11e4-8caf-c622964fbf76.png)

In IE:

![on-ie](https://cloud.githubusercontent.com/assets/4592/3557686/b8ea5194-0932-11e4-8066-8086d8cc4151.png)

As you can see, it uses a bit of JS-based IE detection, and uses a plaintext version for IE. 

It doesn't work well in Firefox's native console, because the stable Firefox channel doesn't yet support fancy formatting. But Firebug is so prevalent in the Firefox dev community that I think that's fine, and Firefox is due to get `%c` formatting support, it's already in the nightly channel, I believe.