[VNFD] [NSD] Add/modify complex interface types

[mbredel]

The type of interface has to specified for the connections points of the VNFCs, the VNFs, and the NSs. Right now, we only support strings to name the type "interface" as an interface-type.

We might want to have more interface types like:

• interfaces
• ports
• VPN endpoints

Moreover, we need to a way to configure these interface types.