Add RemoteSerialConsole support

[jynik]

Add a depthcharge.console.Console subclass that operates on a remote Console instance over TCP.

It may make more sense to re-define depthcharge.console.Console as an abstract base class, with SerialConsole and RemoteSerialConsole implementations. Ideally, this would be done in a backwards compatible way that doesn't break existing scripts.

The use-case for this is remote access to lab environments or shared devices. This can assume the connection is already tunneled by an appropriately authenticated and encrypted channel (e.g. SSH), and only provide a simple TCP interface.