Added edit function in 'album/:id' pages.

-Edit allows you to change the column fields of each song.
-Added method update in song_repo. This method updates every field of the row (which is selected by song_id).
-Added album_id to the build method's properties.
-On get of '/albums/edit/:id/song/:s_id', displays a form with current field value as the default value + an udpate button.
-On post of '/albums/edit/:id/song/:s_id', updates the song information and redirects to the main '/'.
-The main page now sorts the @songs before displaying(implemented due to psql's nature to put the updated row last.