Don't run twice.

Since `dist/Main.js` already evaluates `PS.Main.main` the `onload` runs it again. The other option is to remove the `main` option in the grunt file. Not sure which one makes more sense here.
While we're changing this line anyway, can we assign to `this.onload` instead? Assigning to a variable you didn't declare is a bad practice in JS because it's impossible to know whether it was intentional or an error.