Filter by more extensions/type in file manager

This edit allows to specify more than one value for fType and/or fExtension.

To use it, simply pass an array instead of a string as the value of the filter `fType`/`fExtension` to the `file`, `image`, ... methods of `ConcreteAssetLibraryHelper`.

It may be useful, for instance, to filter video files of type mpeg, which may have an various extensions (mpeg, mpg, m4v, ...), or images that are not gif (filtering for extensions jpg and png).

Please note that the `ccm.app.js` must be rebuilt since I touched one of its components (`filemanager.js`)