UMD Wrapper + Gulp build + Bower/NPM/Component Support

All **tests are passing**.

This **adds a ```gulp build``` task** that **wraps ```pourover.js``` in a [UMD](https://github.com/umdjs/umd)**. 
The result is written to ```dist/pourover.js```.
A minified version is written to ```dist/pourover.min.js```.

Gulp related dependencies are managed by npm, installed via ```npm install```. 
Testing dependencies are now managed by bower's 'dev-dependencies', installed via ```bower install```. 

**Increased compatibility** was the primary motivation for this pull request, my issue was that PourOver assumes underscore is available globally as ```_```.

I am attempting to use PourOver in an environment where ```underscore``` is loaded via a module loader, and therefore it is not available globally as ```_```. Wrapping PourOver in a UMD lets it take advantage of the module loader when it is present, while **transparently falling back to the original behavior** if it is not.