New global value: Essepage.devMode

An Essepage global value, Essepage.devMode, has been added to distinguish between development and production environments.

The usage is as follows:

if ( Essepage.devMode ) {
  console.log("Currently in development mode");
  // Perform development-specific operations
} else {
  console.log("Currently in production mode");
  // Perform production-specific operations
}