Fixed MySQL driver name for legacy minecraft

Fixed potential exception if changes the default table name

Added support of custom MySQL table name
Code cleanup

Optimized skull saving
Skulls with the same skin are now stackable

Fixed SQL auto_increment number goes crazy a little bit (minimal bug)
Don't need to redownload if you are not so obsessive;

now the skin won't be saved as steve if fail;

Now the plugin will get the premium skin of the player if the player has no custom skin(300 skulls per 10minutes due to the Mojang rate limit)

Added support for legacy version 1.8-1.12

Added MySQL storage support
update the plugin and edit the settings in mysql.yml
and restart the server or use plugman to reload
the old data in config.yml will be auto imported