Desktop notifications

The first three patches are about changing the format of "new update" messages.  This is something I wanted to do anyway, but this is the first real user of it.  The new format should help with future backbonification as well as downstream app use when we're ready for that.  It should also be more robust to adding new data. The patches are structured for live deployment.

The final patch adds optional desktop notifications for new updates. The checkbox for the updates is an ugly hack at the moment pending simultaneous design changes that will give it a proper place to land.  The notification icon is the 32x32 (actually it's 31x31 with a blank border top/left) from the reddit.com favicon.ico; I'm amenable to replacing it with something better.  Chrome seems to want 32x32 but firefox looks like it could go larger.

![notifications](https://cloud.githubusercontent.com/assets/338853/2650468/404b4b0c-bf73-11e3-824a-016aebd3c842.png)


:eyeglasses: @chromakode @powerlanguage