Pull dependencies via web, create mozart-rails asset manifest for easier usage 

:information_desk_person: The intent of these changes is to make life easier for users of the `mozart-rails` gem. 

The biggest benefit is adding a `mozart-rails` asset manifest, which means that a user can just add `//= require mozart-rails` to their `app/assets/javascripts/application.js` file and Mozart and all of its dependencies will get magically included. :sparkles: 

* Removes git submodule for mozart dependencies
* Adds new :clean rake task to remove old dependencies
* Adds new :download rake task to pull JavaScript files from web
* Removes :copy_source_files rake task
* Adds new class for paths constant (not ideal)
* Adds new mozart-rails asset manifest for cleaner and tidier usage
* Updates JavaScript dependencies, adding minified versions
* Updates README
* Bumps gem version to 1.0.1