Removed "id" from "alternate_author"
 Converted all instance properties for WPPM_Container class to UPPERCASE to avoid conflict as JSON conventions never(?) use ALL UPPERCASE.
- Added $singular_type_name and $plural_type_name properties to WPPM_Package for convenient access inside HEREDOCs in commands.
- Added initial execute() method for WPPM_Status_Command.
- Added show() method for WPPM_Command.