Delete player in a PGN file

[fsmosca]

• [x] Create "Delete Player" submenu under Tools menu on Neutral mode.
• [x] Create new window when Delete Player is pressed.
• [x] Create Text, Input, and FolderBrowse elements for pgn loading.
• [x] Create Listbox element to display player names from the PGN file.
• [x] Create OK button.
• [x] Read pgn file and extract player names and show it in Listbox.
• [x] If user selects a player from Listbox delete that player when user pressed OK button.