Add drag and drop options for playlist

...as/playpad/layout/desktop/pad/DesktopPadDragListener.java

...n/java/de/tobias/playpad/pad/drag/PlaylistDragOption.java

.../main/java/de/tobias/playpad/view/FileDragOptionView.java

PlayWall/src/main/resources/lang/_de.properties

PlayWallCore/src/main/java/de/tobias/playpad/pad/Pad.java

...java/de/tobias/playpad/pad/content/PadContentFactory.java

...in/java/de/tobias/playpad/pad/drag/ContentDragOption.java

...d/plugin/content/pad/ContentPlayerPadContentFactory.scala