LPS-39474 Video refactoring and add audio to media plugin

Hi Iliyan,

here is the refactor of the plugin. I basically renamed the plugin from "video" to "media", and tried to reuse as much code as possible, and then use that code from the dialogs.

There is no problem in having one file for each dialog (audio.js and video.js), because, as stated in CKEditor documentation these files are only obtained on demand (when clicking in the toolbar button). And makes code much cleaner.

Thanks!