Spice.failed() frontend notice

This should make it much clearer when your Spice (or any others) have called `Spice.failed()` by adding a div to the page indicating what's happened - rather than seeing a blank page.

Ex.
![hacker_news_asdfghjkl123456789_at_duckduckgo](https://cloud.githubusercontent.com/assets/873785/5208293/dd2c77ca-7580-11e4-97e1-b2292e97c408.png)

![hacker_news_asdfghjkl123456789_rubygems_at_duckduckgo](https://cloud.githubusercontent.com/assets/873785/5208304/07fdfbf4-7581-11e4-9b64-9db43d7fa7d8.png)


//cc @russellholt @jagtalon @killerfish