Rework the IPtrunk model

Resolves an issue with lists of interface names and descriptions in coredb getting jumbled.

Now, the LAG members' name and description are bundled together in a new product block: IptrunkInterfaceBlock

requested review from @neda.moeini

assigned to @simone.spinelli

mentioned in merge request !83 (merged)

Eclipsed by !83 (merged), closing this issue

closed