Issue #50 Rule redefinition

* Added Composite pattern on Rule and RuleGroup
* Added new Expression entity
* Fixed factories and repositories
* Fixed tests
* Fixed DataFixtures
* Added RuleManager Configurators
* Created tags "elcodi.rule_expression_language_configuration" and "elcodi.rule_context_configuration"
  to create new ExpressionLanguage configurators.
* "elcodi.rule_expression_language_configuration" allow to create new ExpressionLanguage functions
* "elcodi.rule_context_configuration" allow to create new Context variables for ExpressionLanguage