App: Adapted PingApp to send pings only between start and stop and when the node is up.

Added test cases for all combinations of node startup/shutdown and ping app start/stop sequences.
App: Adapted IPvXTrafGen to Lifecycle operations.
App: Adapter EtherAppCli and EtherTrafGen to lifecycle operations.
App: Adapted DHCP to Lifecycle operations.
Test: Added a few simple positive lifecycle operation tests for StandardHost.
NodeStatus: Changed to allow specifying initial status in lowercase.
Fixed issues when node is initially down.
App: Changed stopTime to use -1 to run the application forever.
App: Adapted two simple TCP applications to lifecycle operations.
Ethernet: Adapted to lifecycle operations.
Lifecycle: Added LifecycleNotSupported base class.
App: Added LifecycleNotSupported base class to some applications.

All application must either support lifecycle operations properly or
throw an error when executing any lifecycle operations.