Custom variables and content in start scripts

SPC replaces some default values with server pack specific information, examples:

MINECRAFT_VERSION="SPC_MINECRAFT_VERSION_SPC";
MODLOADER="SPC_MODLOADER_SPC";
MODLOADER_VERSION="SPC_MODLOADER_VERSION_SPC";
ARGS="SPC_JAVA_ARGS_SPC";
JAVA="SPC_JAVA_SPC";
FABRIC_INSTALLER_VERSION="SPC_FABRIC_INSTALLER_VERSION_SPC";
QUILT_INSTALLER_VERSION="SPC_QUILT_INSTALLER_VERSION_SPC";
MINECRAFT_SERVER_URL="SPC_MINECRAFT_SERVER_URL_SPC";

Allow users to add custom ones on a key,value,origin-basis globally and on a server pack-by-server pack basis:

• Global:
  • All scripts receive this global configuration
  • Said global configuration is stored in the application properties
• Specific:
  • The start scripts for the affected server pack receive this configuration
  • Said configuration is stored in the server pack config