Re-work the reality layer

[magicnat]

The current design of the reality layer does not fit into the layered design and needs to be reworked. It is more like a utility class. Some of its API take an AS instance from another layer, some return an AS instance. It does not seem to fit the layered design.

The reality layer has initially been making changes as the emulation renders. However, changes introduced when ew "decouple" the references between layers have made it impossible to do it the old way and therefore this un-layered design.

• Implement RemoteAccessProvider interface.
• Implement OpenVpnRemoteAccessProvider.
• Add enableRemoteAccess method on the Network class.
• Add createRealWorldRouter on the AutonomousSystem class.
• Rewrite examples and documentation.