Applied changed according to suggestion of code review and Added the implementation to solve sudoku using the algorithm Norvig

- Applied changed according to suggestion of code review
	* Added local variables in the unit test
	* Added a new config.xml in order to use in the unittest
	* Added new validation for the path (exist_path())
	* Added some comments in order to separate the constants variable according their functionality
- Added comment to methods according to PEP 257
- Updated the methods in order to keep the standard PEP 8
- Added the utils module in order to reuse some methods in other classes

- Added the implementation to solve sudoku using the algorithm Norvig
	* Added the AlgorithmBase Strategy interface
	* Added the AlgorithmSolver context
	* Added the AlgorithmNorving class
	* Added the unittest for the AlgorithmNorvig solver method