Add NVV to PickNetworkProviderActivity

This network was missing from the list of network providers, although it was in [pte since August 2011](https://code.google.com/p/public-transport-enabler/source/list?path=/enabler/src/de/schildbach/pte/NvvProvider.java&r=d2cd0b6603a344efd035cdff1591428c9ee8f54f).
I already tested it, by building Liberario myself and everything ran fine.