Continue factoring frontend code out of the main app module

[kalilsn]

The core app.js file, which is the entrypoint for the whole frontend application, is almost 400 lines. There's a lot of logic in there that could be named and encapsulated in a function for readability. It also includes some anonymous functions that should be named.

We should break as much code as we can out of that module and name any discrete pieces of logic, purely for readability. We shouldn't do this until we've written tests for the existing functionality in #42