Binding reqs with caps

[jsoldani]

The prototype is currently assuming that the given TOSCA YAML files are such that each requirement of each node template indicates

• the name of the node template satisfying such requirement (through the field node of the requirement assignment), and
• the name of the capability satisfying such requirement (through the field capability of the requirement assignment).

E.g.,

requirements:
    - endpoint:
        node: backend_api
        capability: endp
    - endpoint
        node: utils_api
        capability: endp

(with backend_api and utils_api both offering a capability named endp)

This is needed to permit deriving the binding between reqs & caps, needed to analyse the management of an app with management protocols