Enhancement: Audio metadata panel

We've added a right sidebar panel with the name `Audio Info`, which display `audio` metadata if present on the given resource.
It is registered by the files app and becomes visible in the global right sidebar in all file contexts, e.g. file listing 
with single select on an audio file with indexed id3 information or when listening to an audio file in the preview app.

https://github.com/owncloud/web/pull/10956
