Moved init of Config class away from ctor

Now the initialization must be done by the caller. This is necessary because Python doesn't have function/method overloading and two different ctors would be necessary to initialize the Config - the first ctor would have to parse the metadata, command and schedule from a string. The second one would accept explicit parameters.
Refactoring

Refactored Config::is_yabm_job to Config::is_config
Refactoring

Refactored core.py into two separate files - config.py and cronmanager.py. These new files contain the classes related to Config and CronManager, respectively.
Small refactoring and comment changes
Implemented parsing methods

Added a new static method (get_value) to retrieve the value for any given key within the metadata using regular expressions.
Refactored is_config static method to use get_value method
Implemented parse_metadata and parse_command method
Refactoring and new features

Added the __str__ method to ConfigSchedule, Config
Saving a reference to the cron job within the Config itself
Minor bugfix on return group index (regex)