Do not offer to add directories in playlist editor if they are contained completely in the playlist already
Hide "add" button for files, too
When reading a playlist, remove the newline characters for easier parsing
Fixed #32: Prevent Oyster from being started multiple times
Merge pull request #33 from speutel/issue32

Fixed #32: Prevent Oyster from being started multiple times
Merge pull request #30 from speutel/mark_files_in_playlist_editor

Mark files in playlist editor
Merge branch 'master' into update_control_buttons