Remove playlist function.
Movie is separate, there's no need for a playlist.
playlist function will be supported in project DShow which is for watching TV shows. DShow's playlist is definitely not this simple.

The following symbols are removed:
TAG_ITEM
TAG_CATEGORY
appendCategory
appendItem
addFile
file_monitor
readFrom
writeTo
importDone
importItemFound
getAllCategories
getAllItems
playNextOf
playPreviousOf
playPrevious
play_sequence_sub_menu
play_sequence
play_next
playerPlayOrderType
ORDER_TYPE
getRandom
getNextSource
getNextSourceCycle
getPreviousSource
getPreviousSourceCycle
_play_operation_next
_play_operation_previous
startWidthFile
NextButton
PreviousButton
open_dir
add_playlist_item
import_playlist
export_playlist
mouseInPlaylistArea
mouseInPlaylistTriggerArea
addPlayListItem
addPlaylistStreamItem
open_folder_dialog
playlistPlay
addItemToPlaylist
addFolderToPlaylist
removeItemFromPlaylist
removeInvalidItemsFromPlaylist
playlistClear
playlistShowClickedItemInFM
playlistInformation
playlistExport
playlistImport
openDir
playNext
togglePlaylist
showForPlaylist
hideForPlaylist
playlist
addtional commit
pyflakes and pep8 fix.

next step:
1. Image files for playlist are not yet removed.
2. The ControlBar layout should be changed because the "previous" button and "next" button are removed.
3. I prefer change to a layout similar to Microsoft Media Player 9.