Many changes performed. Please read the details.

config.py:

ConfigSchedule
- refactored constructor: parameterless ctor
- added __str__ method
- correctly implemented serialize/deserialize

ConfigCommand
- added parameterless ctor
- move __str__ impl to serialize() (new method)
- correctly implemented deserialize method

Config
- Major refactoring

cronmanager.py:
- Almost rewrote the entire file

tests.py:
- Created a new file to add test functions

yabm.py:
- Removed all dummy calls (previously used for test purposes)
- Refactored everything that used to be a test to tests.py in a better test format