[CGMZ] Battle BGM Control - Version Alpha R3

Hi all, today this plugin was updated to version AlphaR3!

This version the plugin has changed away from using a plugin command to control whether the plugin is active to a simple game switch. This should be easier to use. As a result, the Set Control plugin command has been removed.

This update also added theme weights so you can make certain themes more likely to be heard. You could use this to add a rare theme as well.

The map parameter has been converted from a number to map type. This will be much easier for users of MZ 1.9.0+. If you are not yet on 1.9.0, you can manually enter the map id as before.

• Added theme weights
• Added game switch to control plugin functionality
• Removed Set Control plugin command
• Map parameter converted to map type