With this commit, we change the delivery method for the ACE editor from manually copied files to using yarn and webpack. As a side-change, we also modify how the mode is selected through JavaScript instead of Ruby.
Through webpack, the `modePath`, `themePath`, and `workerPath` are automatically determined and working as expected.
Closes#250
Since we switched to more I18n-JS and JsRoute functions with f5739a33 and 2f03061f, we don't have the need to use a template engine for those files any longer.
