Moved up name attribute to Definition to allow creation of PropertiesSpecifications independent of the fact we are using Data or a Type. #54

Introduced base::Definition to have a common ancestor for TypeDefinition and DataDescription. This is necessary to better implement #53 in EvoAl.

Besides of declaring the possibility of 'data or type of instance', we have to introduce a new rule for adding a type definition reference. Therefore, we introduced a InstanceDefinitionReferenceRule. #53

Using SHELL environment variable to find the system shell on non-windows OSes. The fall back is 'bash' if the variable does not exist.

Make all search path entries absolute to avoid lookup problems while importing DSL files from each other.

Added a validation rule that checks if the storage path of a module is correct (package/filename structure).

Added a getFilename() method to model element Import that calculates the correct filename. Make use of this function in the ClasspathGlobalScopeProvider to avoid duplication of code.