Fix: router works when refreshing a URL fragment

Turns out that Backbone.history.start() reads the current fragment and
calls the router function for it.  This meant that it was trying to show
the current page before it had rendered.
Refactor: move Router creation to main

The router is now created above app.js, in main.js.  App.js is meant to
be the main view of the app, so it has no business creating routers and
starting Backbone history.
Add comments

Add comments to app.js to explain what each bit is doing
Refactor: rename variable in app.js

template -> navigationTemplate, to better indicate what it is
Default to Splashscreen page

If we're not on a page yet, navigate to the Splashscreen page
Hang onto app for later
Update readme

We have a router now
Fix: link to nonexistent favicon

Not sure where I got this line from, but I certainly don't have that
favicon anywhere! :0