[Fork 6] - MediaLibrary

[absumo]

Implement the MediaLibrary module in Fork6

Backend

Keep same functionality, containing MediaItem, MediaFolder and MediaGroup.
Add/Document config options to easily enable certain LiipImagineBundle filters.
Optionally use an external FileUpload bundle instead of our custom UploadHandler.
Replace fine-uploader and cropper because they are deprecated.
Remove jQuery dependency.

Frontend

Copy the existing widgets.
Upgrade photoswipe.js