TOSCA types requirements should be a dict instead of list

The current specs in revision doesn't clearly distinct Requirements definition for node templates and node types. The current code defines requirements as 'list' in the service (node) template and node types. Using 'list' is a correct notation for template but for types it should be dictionary. Specs will be changed for better readability with some examples and the code will need be to changed accordingly. The changes includes the TOSCA_definition.yaml file and other .yaml files created for custom types.