Implemented the feature where, the media files directly opened into the
playlist from the "open" button will be parsed and added automatically
into the library/database and shown in alphabetical order.

Also fixed the bug where when a media is first loaded into the playlist
through either the "open" button or dragging/doubleclicking within the
library window, pressing the playbutton does not play the media.
-- Fixed by creating a new "mediaAvailable" SIGNAL-SLOT pair in
playlistModel.cpp and player.cpp.