Added browserify test & build task, updated UMD definition.

The UMD definition in #436 was close but had an issue with [L11](https://github.com/tbranyen/backbone.layoutmanager/commit/ca5a3edf0397738058e6d3194461740832ec4b33#diff-ba55fcfab2e1723ff437c1eec10d55e4R11). This line could actually be stricken as the var was never used.

This PR cleans up the UMD definition, moving the browser definition into the `else` block. Additionally, I removed the explicit bind to `window.Backbone.Layout`, as it is already exported on [L834](https://github.com/tbranyen/backbone.layoutmanager/blob/ca5a3edf0397738058e6d3194461740832ec4b33/backbone.layoutmanager.js#L834).

This PR also adds a browserify build task and a basic test to ensure template rendering works with the browserified build.