Big update! This update adds support for getting data from a database and from placeholders, and drops support for MC 1.15

• New data source: MySQL database
  
• New data source: PlaceholderAPI
  
• Hide entries without scores (prevents armour statues books from showing)
• Allow bypassing the plugin and use your own data source
• Remove /scoreboard.json endpoint
• Add api-version: 1.16 to plugin.yml
  
• Log IP address on URI parse error
• Use logger instead of System.err