Stop loading skin js/css and language files automatically 

As is documented [here](https://github.com/wymeditor/wymeditor/blob/0edd6556d544fcc0ebbe7aa368b090a5608152a7/docs/customizing_wymeditor/index.rst#no-more-skin-auto-loading), skin auto-loading is no longer worth the performance/complexity/magic trade-off for a small ease-of-use gain. We can regain the ease of use by modifying the build to automatically bundle all of the necessary skins (and further, by stopping the use of pop-up windows for dialogs).

We should also include all of the languages in the build. No need to do an extra HTTP request for that.