Boards with failed-to-load parsers should still show up in the board list

[zethon]

• add a board with a Lua parser
• confirm the board was added successfully and shows in the board list
• remove the Lua parser and restart Owl
• the board "disappears" from the board list

This is because MainWindow::loadBoards() will catch any "Fail to create parser of type" errors. Ideally the board would still show in the board list with some kind of visual indicator that it failed to load.