SwitchPortStatistics contains Map<String,PortStatistics> instead of Map<Integer,PortStatistics>

All uses of this class have been updated.
Merge branch 'refactor/switch-port-statistics-use-string' into feature/net-statistics-uses-topology-elements
NetStatistics retrieves information only from devices in that network.
Merge pull request #844 from isartcanyameres/feature/net-statistics-uses-topology-elements

Feature/net statistics uses topology elements