prevent running migrations if is_fresh_install

+ fix: sqlite3.ProgrammingError: Cannot operate on a closed cursor on ProcessAlbumColors()
+ move processing artist images from periodic_scans to Populate
+ bump hash string limit from 7 to 10
+ add last_mod property to database
+ fix: TypeError: '<' not supported between instances of 'int' and 'str' on album page

app/db/sqlite/artists.py

@@ -21,7 +21,6 @@ class SQLiteArtistMethods:
             """
         colors = json.dumps(colors)
         cur.execute(sql, (artisthash, colors))
-        cur.close()
 
     @staticmethod
     def get_all_artists():