Added Last_Seen Column

Added a new column, Last_Seen, which shows the user when the last time,
most recently, a song was playing.
Added Last_Seen Column

Used to catch the last, most recent, time a song was caught playing.
Added Last_Seen Updates/Inserts

Added a new column to the insert/update scripts, so that a user can see
when a song was most recently played instead of only knowing when it
first appeared.