This commit prepares the frontend code to be consumed by webpack.
It is a hack: In theory, modules should be declaring and importing the
modules they depend on and the globals they expose directly.
However, that requires significant per-module work, which we don't
really want to block moving our toolchain to webpack on.
So we expose the modules by setting window.varName = varName; as
needed in the js files.
$.browser is not supported in higher versions of jQuery. The solution
is to instead use vanilla JavaScript to test the navigator.userAgent
property for the browser.
Fixes: #1033.
Armaan Ahluwalia
Tim Abbott
Brock Whittaker
Steve Howell